Gas Caps

July 13, 2014

Contents: 01. Quarter-turn 27mm thin wing
Contents: 02. Quarter-turn 30mm  
Contents: 03. Quarter-turn 30mm thin wing    
Contents: 04. Quarter-turn 40mm   
Contents: 05. Quarter-turn 40mm thin wing
Contents: 06. Quarter-turn 40mm wide wing
Contents: 07. Quarter-turn 40mm external wing
Contents: 08. Push-in xxxx 30mm   
Contents: 09. Push-in xxxx 32mm     
Contents: 10. Push-in xxxx 36mm   
Contents: 11. Push-in xxxx 40mm   
Contents: 12. Screw-on  M30-1.75 external thread  
Contents: 13. Screw-on  M40-1.75, 2.0 external  
Contents: 14. Screw-on  M42-1.50 internal thread 
Contents: 15. Screw-on  M50-1.50, 2.0 internal 
Contents: 16. Pop-up (moped)
Contents: 17. Information and Explanation




1. Quarter-turn 27mm

1a qtr-turn 27 thin wing $32
Trac Liberty step-thru

Gas tank qtr turn 27mm Trac Liberty

1984-89 Trac Liberty
quarter turn 27mm

Gas tank qtr turn 27mm (35 mm wing to wing) Trac Liberty

1984-89 Trac Liberty
35mm wing to wing









2. Quarter-turn 30mm

For quarter-turn gas caps, the named size is the inner diameter of the filler neck it fits into. The actual size of the gas cap is a little less than the named size. That’s why a 28mm gas cap on the internet is called 30mm here, or a 38 is called 40 here.  

1. 1/4 turn 32mm chrome bottom view

2a q-turn 30 chrome $10
generic 206401

1. 1/4 turn 32mm chrome top view

qtr-turn 30mm
chrome, top view

1a. Rubber washer 30x50x2

2b Rubber washer $1
30 x 50 x 2mm for
most 30mm qtr-turn

1a. Buna rubber replaces old cork

Rubber replaces cork
on most 30mm gas lids










2c qtr-turn 30 black $22
Tomos 222145
1985-93 Golden Bullet

54. qtr-turn 30mm Tomos orig on 1980-90 Bullet

2d qtr-turn 30 aluminum
1979-91 Tomos Bullet
(for reference)

3a. qtr-turn 30mm alum original on 1976 Tomos

2e qtr-turn 30 alum. $25
1974-78 Tomos Bullet
(can be polished)

3b. qtr-turn 30mm Tomos L orig on 1980 Bullet R orig on 2000 Sprint

qtr-turn 30mm Tomos
2f from 1980 Bullet $12
2g from 2000 Sprint $22










Puch Maxi tank qtr-turn 30mm

1978 Puch Maxi
qtr-turn 30mm

Puch Maxi tank push-in 32mm

1976 Puch Maxi tank
push-in 30mm

Garelli Super Sport tank quarter-turn 32mm

1978 Garelli Super Sport tank
quarter-turn 30mm gas cap
(77 and some 78 are screw-on)










2. 1/4 turn 32mm locking

2h qtr-turn 30mm $17
chrome locking, 2 keys
Tomos 229530

21. qtr-turn 32mm chrome Garelli

2i qtr-turn 30 new $30
orig on 1978-on Garelli

2j qtr-turn 30mm new $60
Puch chrome with cup











7. qtr-turn 32mm used Puch w/cup

2k qtr-turn 30mm $20-40
chrome Puch used
with oil measuring cup

8. qtr-turn 32mm used alum Puch

2l qtr-turn 30 $15-30 
aluminum Puch used

12. qtr-turn 32mm chrome Puch used

2m qtr-turn 30 $15-30
chrome Puch used










3. Quarter-turn 30mm thin wing

Some of these have thinner wings, and some have slightly different wings than “regular”.

48. qtr-turn 30mm Honda NC50 Express has vent on/off

3a qtr-turn 30mm used  N/A
Honda NC50 Express
has vent on/off switch

49. qtr-turn 30mm w/cup Honda PA50 Hobbit

3b qtr-turn 30 thin used $25
Honda PA50 Hobbit
has oil measuring cup

51. qtr-turn 30mm chrome Angel (Taiwan)

3c qtr-turn 30 used $20
Angel (TYM Taiwan)
slightly different wings










3d left, qtr-turn 30 thin  $18
1970’s Suzuki, no gasket

qtr-turn 30 & 40 thin wing
L is 30mm with no gasket
R is 40 w/leather gasket










4. Quarter-turn 40mm

For quarter-turn gas caps, the named size is the inner diameter of the filler neck it fits into. The actual size of the gas cap is a little less than the named size. That’s why these are called 40mm here, but they are called 38mm elsewhere. 

10. qtr-turn 40mm chrome with qtr-turn 32mm

4a left, qtr-turn 40mm chrome $12
generic 632610 (right is 30mm)

4. qtr-turn 40mm black orig on 1987-91 Tomos Golden Bullet TTLX

4b qtr-turn 40mm black $15
Tomos 222785
1987-91 Golden Bullet TTLX

4c qtr-turn 40 used $25
Sears Free Spirit, Murray










4d qtr-turn 40 used $40
Sears, Murray with cup

6. qtr-turn 40mm black locking

4e qtr-turn 40 black locking $25
Tomos 229545
1996-13 Tomos LX top tank

20. qtr-tur 40mm chrome locking

4f qtr-turn locking $17
Tomos 223840
1987-91 Bullet TT










4g qtr-turn 40 $20-$55
Puch Magnum









5. Quarter turn 40mm thin wing

18a. qtr-turn 30 & 40mm L is 1970's Suzuki 30 R is 1970's Japan 40

5a right, qtr-turn 40 $35
L is 1970′s Suzuki 30
R is 1970′s Japan 40

18a. qtr-turn 30 & 40 thin L is 30 with no gasket R is w/leather gasket

same ones bottom
L is 30 with no gasket
R is 40 w/leather gasket

46. qtr-turn 40mm Trac

5b qtr-turn 40 thin $35
1985-87 Trac Hawk

47. qtr-turn 40mm ?? Trac DH100 top tank?

5c qtr-turn 40 thin $35
1986-88 Trac DH100









6. Quarter-turn 40mm wide wing

41 and 26 look the same on top

6a stainless, and 7a chrome
are the same on top

41 and 26 are very different on bottom

6a 40 wide and 7a external
are very different on bottom








41. qtr turn 40mm wide wing regular wing at right

6a qtr-turn 40 wide wing $30
regular wing at right
Pacer top tank (some)

1979 Motobecane Sebring qtr-turn 40mm wide wing

1979 Motobecane Sebring
qtr-turn 40 wide, lid 6a










7. Quarter turn 40mm external wing

26. qtr-turn 60mm chrome Peugeot TSM

7a qtr-turn 40 external $30
chrome Peugeot TSM

26. qtr-turn 60mm bottom view

qtr-turn 40mm external
view of external wings
Pacer top tank (some)

23. qtr-turn 40 external black locking

7b qtr-turn 40 external $30
black locking for TSM

7c qtr-turn 40 ext.
Peugeot TSM








41 and 26 look the same on top

6a stainless and 7a chrome
are the same on top

41 and 26 are very different on bottom

6a 40 wide and 7a external
are very different on bottom

1980 Peugeot TSM tank qtr turn 40mm external

1980 Peugeot TSM
q-turn 40 external

Vintage motorcycle tank qtr-turn 40 external wing

Vintage tank
qtr-turn 40 external
takes lid 7a









8. Push-in 30mm

The named size of push-in gas caps is the inner diameter of the filler neck, 30mm. The actual size is smaller, 28 or 29 so it can slide in. But the seal lip or rubber ring is bigger 31mm, so it can get squeezed as it pushes in.

8a push-in $12 30mm generic

32. push-in 30mm Cimatti

8b push-in 30mm $20
pre-’78 Cimatti City Bike
(’78-on was qtr turn)

33. push-in 30mm Peugeot

push-in 30mm, left: 8c Peugeot 103 original N/A
right: replacements plain and Esso $35
These shrink. Adding an o-ring 8d fixes that $2










29. push-in 30mm early Puch original

8e push-in 30 $30
early Puch original

18. push-in 30mm Hercules/Sachs

8f push-in 30mm  N/A
early Hercules-Sachs P1, M4
later Sachs tanks had qtr-turn

31. push-in 30mm KTM Foxi original

8g push-in 30mm $40
’77-79 KTM Foxi Deluxe

31. KTM caps break easy

KTM caps break easy
8h repaired but fragile $10
8g new kept in plastic bag











Peugeot 103 gas tank push in 30mm gas lid

1978 Peugeot 103 tank
push in 30mm gas lid

1980 Peugeot 102 tank 30mm push-in improv lid

1980 Peugeot 102 tank
30mm push-in improv lid

55. push-in 30mm locking - Avanti

8i push-in 30mm N/A
locking for Avanti

52. push-in 30mm with large teardrop top

8j push-in 30mm $25
with large teardrop top
Gitane Cricket (Testi)









45. push-in 30mm black Colombia Open Road

8k push-in 30mm $25
Colombia Open Road

45. push-in 30mm Colombia left shrunk, right new

push-in 30 Colombia
left shrunk, right new

8l push-in 30mm $35 Peugeot locking gas cap








9. Push-in 32mm

The push-in gas caps 9a, 9c, 9d, 9f have a thick rubber ring that is made too large, 34-35mm. Right out of the package it is too big to enter a 32mm gas tank filler neck, even with grease and care. The rubber ring must be ground down to reduce the outer diameter to 33mm. This makes the price a few dollars more.

9a 32mm push-in $17
with rubber ring ground
to 33, to fit 32 correctly
(shown with no rubber)
5313-N with dip stick

26. push-in 32mm Derbi shows how some shrink to 30mm

push-in 32mm Derbi
some shrink to 30mm!

26. Derbi 8204140 gas lid left - '76-86 not shrunk right - '86-89 shrunk to 30

Derbi 8204140 gas lid
left 9b ’76-86 not shrunk $35
rt – ’86-89 shrunk to 30

Derbi Variant tank 32mm

1977-89 Derbi Variant
32mm push in lid











It’s amazing how much that Derbi gas cap shrank, from 32 to 30mm. And how the one from the newer model shrank, but the older model one did not. So a badly shrunken one could fit nicely on a Peugeot! Other soft plastic push-in gas caps with lips, not rubber rings, also shrink, like Peugeot. Only those 35 year old NOS ones that have been kept in a sealed plastic bag are not shrunk.


30. push-in 32mm Tomos Revival

9c push-in 32mm $20
Tomos 232546
’02-09 Revival, Streetmate
after 09 was qtr-turn 30
includes proper 33 ring

Special rubber washer fits Garelli and Tomos 32mm push in gas caps, with some grinding.

9d Rubber ring (buna-N) 35mm not ground $3
fits Tomos and Garelli 32mm push in gas lids 9e with the outer surface ground down to 33 $9
L to R, no rubber, rubber not cut, rubber cut


35. push-in 32mm early Garelli missing the o-ring

9f push-in 32mm $35
early Garelli step-thru
(shown with no o-ring)
includes proper 33 ring












2005 Tomos Streetmate with 32mm push in lid until

2005 Tomos Streetmate
with 32mm push in lid
until 2010 then qtr-turn









10. Push-in 36mm

27. push-in 36mm Derbi Laguna

10a push-in 36mm N/A
Derbi Laguna, RD50










11. Push-in 40mm

28. push-in 40mm Gitane/Testi

11a push-in 40mm N/A
1976-78 Gitane (Testi)

39. push in 40mm 1970's Jawa original

11b push-in 40mm $30
1970-83 Jawa step-thru

General top tank pop-up accepts 40mm push-in

1979 General top tank
accepts 40mm push-in










12. Screw-on 30mm

13. screw-in Motobecane 1. dull used 2. shiny used 3. with vent on/off

12a,b,c screw-on 30×1.75
71-80 Motobecane 40, 50
a dull used w/stick $30
shiny good used $45
c with vent switch $35

14. screw-in Motobecane chrome locking

12d screw-on chrome
30×1.75 ext thread $40
Motobecane chrome locking with two keys

37. screw-in male Motobecane new white plastic

12e screw-on plastic
30×1.75 ext thread $30
for Motobecane 40,50











1979 Motobecane 50V screw on male M30 x 2 tank ID is 28.5mm

1979 Motobecane 50V screw on male 30×1.75
tank ID is 28.5mm

Same MB tank cut away

Same MB tank cut away
inside view of fill hole
& center bulkhead wall












13. Screw-on 40mm

1978 Vespa Ciao tank screw-on female M40x2 with PVC improv lid

13a screw-on int 40×2
with PVC improv lid

1978 Vespa Ciao tank PVC improv lid open

1978 Ciao tank
PVC improv lid

Close up of PVC lid made from a 1-1/4" PVC threaded cap sliced in half

M40x2 female PVC lid
made from a 1-1/4″
PVC threaded cap
sliced in half

15. screw-on not vented AMF Roadmaster (R eng)

13b screw-on int. 40×2
not vented $15
AMF Roadmaster with McCulloch rear engine










16. screw-on fem M40x2 Vespa Ciao,Bravo,Grande

13c screw-on M40x2 $25
orig on Vespa (Piaggio)
Ciao, Bravo, Grande

16a. screw-on fem 40x2 L is white PVC improv R is aluminum original

screw-on internal 40×2
L is white PVC improv
R is aluminum original

16a. screw-on fem 40x2 PVC 1-1/4" cap is 38.5 ID fits 40x2 well, by luck!

screw-on internal 40×2
PVC 1-1/4″ cap is 38.5 ID
fits 40×2 well, by luck!

16b. 1-1/2 PVC is too big for 40 (38.5id), too small for 50 (48.5id)

1-1/2 PVC is too big for 40 (38.5ID), too small (45.0ID) for 50 (48.5ID)










1978 Vespa Bravo tank screw-in female M40x2

1978 Vespa Bravo
screw-on M40x2 internal

1968 Lambretino
screw-on M40x2 internal

37. screw-on M40x1.75 white, for MB Model 7

13e screw-on 40×1.75 external thread $35
white, for MB Model 7

40. screw in male 40x2

13f screw-on M40x2 external $25










14. Screw-on 42mm

22. screw-in female 42x1.5 Garelli Super Sport these shrink

14a screw-on 42×1.5 int. $40
Garelli Super Sport
early top tank (these shrink)

Garelli Super Sport tank screw-in (female lid) M42 x 1.5 thread

Garelli Super Sport screw-on
internal thread (female) lid
M42 x 1.5 thread

 Early Garelli Super Sport mopeds had this 42mm screw-on gas cap, while later models had 30mm quarter-turn gas caps. The M42x1.5 external threads on the tank measure 41.5mm. The M42x1,5 internal threads on the cap measure 40.5mm. Many of these shrink with age, unless they are kept in a sealed plastic bag. Then the internal diameter decreases from 40.5 to 40.0 or less, and the cap screws on tightly or only partially.



Garelli Super Sport screw-in (female lid)

Garelli Super Sport

53. screw-on M42x1.5 with vent close switch orig on Italjet Packaway

14b screw-on 42×1.5 internal thread $40 with vent close switch ’77-79 Italjet Packaway

These gas lids are not shrunk because they were kept in a plastic bag for 40 years. Others that are shrunk are offered at half price. Those were exposed to the air for 40 years.

Almost all moped gas caps are vented. Some have a vent switch. When you transport the bike laying on it’s side, gasoline drips out of the air vent hole in the gas cap. With a vent switch you can close the vent hole during transport or storage, and open it during regular use. 





15. Screw-on 50mm

42. screw on female M50x1.5 for Demm Smily and Italian

15a int. M50×1.5 N/A

42. screw in M50x1.5 bottom view 48.5mm ID

15a screw-on M50x1.5
48.5 ID for Demm Smily
Benelli (Wards Riverside)

42. screw-on fem 50x1.5 orig. on 1960's Aermacchi

15b int. 50×2.5 N/A
orig. on 60′s Aermacchi

Concord XKE










1962? Sears Allstate tank screw-on female gas lid very coarse thread

1962? Sears Allstate tank
screw-on female gas lid
very coarse thread

1965 Harley Davidson M50 tank (Aermacchi) screw-on fem M50x1.5

1965 Harley Davidson M50 tank (Aermacchi)
screw-on fem M50x1.5

15c internal 50×2.0 N/A
1980-88 Vespa Si
(bigger than other models)











16. Pop-up gas caps

3. pop-up clamp-on

16a pop-up clamp-on
for 45mm OD tank $17
Pacer Sport (Italtelai)
Baretta 22,44 (Piccoli)
Westwind (Spisni Lino)

11. pop-up locking chrome General

16b pop-up locking $45
chrome General
new with 2 keys












17. Information and Explanation


More gas caps, not for sale,  for your information:

55. screw-on 40mm coarse for modern ATV

60. screw-on 40mm
very coarse thread
for modern ATV

56. screw-on 50mm very coarse thread for modern ATV

61. screw-on 50mm
very coarse thread
for modern ATV

57. screw-on 50mm very coarse thread for modern ATV

62. screw-on 50mm
very coarse thread
for modern ATV

Modern ATV Gas Caps

Modern ATV Lids











Gas caps come in 4 types. 1. Quarter turn, 2. Push in, 3. Screw on, 4. Pop up. Each type has different sizes.

Quarter turn gas lids on mopeds. L to R, 30, 40, 60mm

30 and 40mm quarter turn “regular wing”, 40mm quarter turn “external wing”. Many other quarter turn wing styles are possible. Two other moped styles are nick named “thin wing” and “wide wing”.

Quarter turn has two “wings” on opposite sides that enter two slots in the gas tank lip. Then when the gas cap is rotated 90 degrees to the right, which is one fourth of a turn, it locks on and seals the outer edge by the spring tension in the wings. The spring has a certain amount of “travel” that allows the lid to work (seal) on a range of gas tank lip thicknesses, or as the rubber or cork gasket gets thin. But sometimes a thicker rubber washer is needed to get the wings to push harder and seal better. In the 30mm size an extra 2mm thick rubber is sold here, but not for 40mm, at this time.

Push in lid gas tanks have a smooth round wall, about as deep as it is wide. The lids are usually black plastic with thin flexible circular ridges that press against the wall. The entrance has a taper for easy operation. In the 1977 USA moped standards, push in gas lids were supposedly required to be quarter turn. Puch, Cimatti, Garelli, and Sachs switched from push-in to quarter-turn but not everyone else did. Again in 2010, quarter turn gas caps are mandated in the USA, this time not for safety reasons, but for environmental ones.


Myrons Mopeds Gas Caps, June 2013 Back row: Quarter turn L to R 27,30,40,60mm Front row: Push-in, Screw-on, and Pop-up

Myrons Mopeds Gas Caps, Class of 2013, click to enlarge.
Back row: Quarter turn L to R 27,30,40,40 mm external
Front row: Push-in 30,32,36,40, Screw-on, Misc and Pop-up

Screw on lid gas tanks have threads. The lid must be screwed on one or more full turns clockwise. The threads on the lid can be either female (internal) or male (external). Most modern screw on lids are more like bottle cap threads, more coarse than machine threads. Also the tops and bottoms of the threads have wide plateaus. Some are at right, not listed.

Pop up gas lids are generally on top tank mopeds and modern motorcycles. Turn the key or push the button and the lid pops open.

Vent Hole: All moped gas caps are “vented”. That means they have a tiny pinhole or channel that lets air get in or out. If the pinhole is blocked, after awhile a suction will develop, the gasoline supply will stop, especially with a full tank. They all have a vent design that prevents gasoline from shooting out, like a wall or a maze, but lets air get through. Some gas caps have a vent switch, “on” or open for riding, “off” or closed for transport and storage. All vented gas lids will leak gas if the tank is too full or leaned over too far.

Shrinkage: Unless they have been kept stored in an air tight bag, many of the vintage moped plastic gas caps shrink after 20 or 40 years. The Peugeot and Colombia black plastic push-in 30mm lids become 29 or 28mm. The 32mm late Derbi black plastic push-in lid becomes 30mm. The Garelli 42mm screw-on black plastic lid becomes 41 or 40. When a push in lid shrinks, it gets loose and falls off. One remedy for that is a “leash” made out of a twist tie. Another remedy is a thin rubber o-ring, but it’s hard to find the correct size. With push-in gas caps, the actual diameter will be slightly more, about 0.5 millimeter, than the tank hole inner diameter, to make a light press fit. So a 30mm lid should be 30.5mm wide, a 40 should be 40.5. With screw on male lids there can be shrinkage and the lid will still function, because it does not seal on the loose threads. But when a female (internal thread) screw-on lid gets smaller, it becomes tight and difficult or impossible to screw on.