updated 2020-03
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 60mm external wing
Contents: 08. Push-in xxxx 28mm
Contents: 09. Push-in xxxx 30mm
Contents: 10. Push-in xxxx 32mm
Contents: 11. Push-in xxxx 36mm
Contents: 12. Push-in xxxx 40mm
Contents: 13. Screw-on M30-1.75 external thread
Contents: 14. Screw-on M40-1.75, 2.0 external
Contents: 15. Screw-on M42-1.50 internal thread
Contents: 16. Screw-on M50-1.50, 2.0, 2.5 internal
Contents: 17. Screw-on “bottle-cap” thread 45mm
Contents: 18. Pop-up (moped)
Contents: 19. Information and Explanation
1. Quarter-turn 27mm
This is a special size gas cap, only found only on some Trac models:
1983-90 Clipper, 1982-86 Eagle, 1984-88 Escot, 1984-89 Liberty, 1986-89 Olympic, and maybe 1988-90 Blitz.
It is part number 21204 or 17620-M56-8900.
A 30mm quarter turn cap is too big and cannot be made to fit by simple grinding.
1a qtr-turn 27 thin wing $32
Trac Liberty step-thru
1984-89 Trac Liberty
quarter turn 27mm
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.
2a q-turn 30 chrome $10
generic 206401
qtr-turn 30mm
chrome, top view
2b Rubber washer $1
30 x 50 x 2mm for
most 30mm qtr-turn
Rubber replaces cork
on most 30mm gas lids
2c q-turn 30 black $17
Tomos 222145
1985-93 Golden Bullet
2d q-turn 30 alum $15
1974-78 Tomos Bullet
2e qtr-turn 30 alum.
add 2% oil to gas $12
2f premix 3oz of oil per
gallon of gas $15
1978 Puch Maxi
qtr-turn 30mm
1976 Puch Maxi tank
push-in 30mm
1978 Garelli Super Sport tank
quarter-turn 30mm gas cap
(77 and some 78 are screw-on)
2h qtr-turn 30 N/A
chrome locking, 2 keys
Tomos 229530
2i qtr-turn 30 new N/A
orig on 1978-on Garelli
2j qtr-turn 30mm new $60
Puch chrome with cup
2k qtr-turn 30mm $20-40
chrome Puch used
with oil measuring cup
2l qtr-turn 30 $15-30
aluminum 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”.
3a qtr-turn 30mm used N/A
Honda NC50 Express
has vent on/off switch
3b qtr-turn 30 thin used $25
Honda PA50 Hobbit
has oil measuring cup
3c qtr-turn 30 used $15
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.
4a left, qtr-turn 40mm chrome $8
generic 632610 (right is 30mm)
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
4e qtr-turn 40 black locking N/A
Tomos 229545
1996-13 Tomos LX top tank
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
5a right, qtr-turn 40 $35
L is 1970′s Suzuki 30
R is 1970′s Japan 40
same ones bottom
L is 30 with no gasket
R is 40 w/leather gasket
5b qtr-turn 40 thin $35
1985-87 Trac Hawk
5c qtr-turn 40 thin $35
1986-88 Trac DH100
6. Quarter-turn 40mm wide wing
6a and 7a chrome
are the same on top
6a wide and 7a ext. are
very different on bottom
6a qtr-turn 40 wide wing $30
wings 46.9 x 12.7mm
regular wing at right
’79 Motobecane Sebring
qtr-turn 40 wide, lid 6a
Pacer top tank (some)
7. Quarter turn 60mm external wing
7a qtr-turn 60 external $30
chrome Peugeot TSM
qtr-turn 60mm external
view of external wings
Pacer top tank (some)
7b qtr-turn 60 external $30
black locking for TSM
7c qtr-turn 60 ext.
Peugeot TSM
6a stainless and 7a chrome
are the same on top
6a 40 wide and 7a external
are very different on bottom
1980 Peugeot TSM
q-turn 60 external
Vintage tank
qtr-turn 60 external
takes lid 7a
8. Push-in 28mm
The early Vespa Ciao, 1967-68 up to frame #154099, had a light gray plastic 28mm push-in gas cap. Myrons does not have any, not even a photo.
After that it was a 32mm push-in.
9. 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.
9a push-in $12 30mm generic
9b push-in 30mm $20
pre-’78 Cimatti City Bike
(’78-on was qtr turn)
push-in 30mm, left: 9c Peugeot 103 original N/A
right: replacements plain and Esso $35
These shrink. Adding an o-ring 9d fixes that $2
9e push-in 30 $30
early Puch original
9f push-in 30mm N/A
early Hercules-Sachs P1, M4
later Sachs tanks had qtr-turn
9g push-in 30mm $40
’77-79 KTM Foxi Deluxe
KTM caps break easy
9h repaired but fragile $10
9g new kept in plastic bag
1978 Peugeot 103 tank
push in 30mm gas lid
1980 Peugeot 102 tank
30mm push-in improv lid
9i push-in 30mm N/A
locking for Avanti
9j push-in 30mm $25
with large teardrop top
Gitane Cricket (Testi)
9k push-in 30mm $25
Colombia Open Road
push-in 30 Colombia
left shrunk, right new
9l push-in 30mm $35 Peugeot locking gas cap
1985 General TE tank
30mm push in gas cap
10. Push-in 32mm
The push-in gas caps 10a, 10c, 10d, 10f 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.
10a 32mm push-in $13
with rubber ring ground
to 33, to fit 32 correctly
(shown with no rubber)
5313-N with dip stick
push-in 32mm Derbi
some shrink to 30mm!
Derbi 8204140 gas lid
left 10b ’76-86 not shrunk $35
rt – ’86-89 shrunk to 30
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.
10c push-in 32mm $25
Tomos 232546
’02-09 Revival, Streetmate
after 09 was qtr-turn 30
includes proper 33 ring
10d Rubber ring (buna-N) 35mm not ground $3
fits Tomos and Garelli 32mm push in gas lids 10e with the outer surface ground down to 33 $9
L to R, no rubber, rubber not cut, rubber cut
10f 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 2010 then qtr-turn
11. Push-in 36mm
11a push-in 36mm N/A
Derbi Laguna, RD50
12. Push-in 40mm
This fits Benelli G2, Moto Guzzi Robin and others.
12a push-in 40mm $14
1976-78 Gitane (Testi)
12b push-in 40mm $30
1970-83 Jawa step-thru
1979 General top tank
accepts 40mm push-in
13. Screw-on 30mm
Screw-on M30-1.75 external thread for Motobecane 40, 50
13a used with M logo, no dip stick none
13b new with M logo, with dip stick $32.0
13c new with vent switch with stick $21.0
13d used with vent switch no stick $15.0
13e new plastic M logo, w/dip stick $28.0
13f used plastic M logo no dip stick $19.0
1979 Motobecane 50V screw on male 30×1.75
tank ID is 28.5mm
Same MB tank cut away
inside view of fill hole
& center bulkhead wall
14. Screw-on 40mm
14a screw-on int 40×2
with PVC improv lid
1978 Ciao tank
PVC improv lid
M40x2 female PVC lid
made from a 1-1/4″
PVC threaded cap
sliced in half
14b screw-on int. 40×2
not vented $15
AMF Roadmaster with McCulloch rear engine
screw-on internal 40×2
L is white PVC improv
R is aluminum original
screw-on internal 40×2
PVC 1-1/4″ cap is 38.5 ID
fits 40×2 well, by luck!
14c screw-on 40×2 internal $32 cnc aluminum
1978 Vespa Bravo
screw-on M40x2 internal
1968 Lambretino
screw-on M40x2 internal
14e screw-on 40×1.75 external thread $35
white, for MB Model 7
14f screw-on M40x2 external $25
15. Screw-on 42mm
15a screw-on 42×1.5 int. $55
Garelli (not shrunk 40.5 id)
Garelli Super Sport screw-on
internal thread (female) lid
M42 x 1.5 thread
Garelli Super Sport
Concord XKE gas cap 41.6 mm at thread tops
15b screw-on 42×1.5 internal thread N/A 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.
16. Screw-on 50mm
16a M50-1.5 internal N/A
“FILL ONCE S.A.E. OIL 30
FOR EACH QT OF GAS”
M50-1.5 int. 48.5 id
for Demm & Wards
Wards Riverside
Demm Smily
16b M50-2.0 internal N/A
1980-88 Vespa Si
(bigger than Ciao)
1980-88 Vespa Si
This cap 16b has the 50mm thread tops on the tank, like 16a and 16c, but the pitch is in between those two.
16c M50-2.5 internal N/A
original on 1965 H.D. M50
1965 Harley Davidson M50 tank (Aermacchi)
M50-2.5 int.thread lid
This cap 16c looks similar to 16a, but threads are coarser. The ridges on top are evenly spaced, but on 16a they are in pairs.
17. Screw-on “bottle-cap” thread 45, 55 mm
1962? Sears Allstate tank
45mm bottle-cap gas lid
A Blitz gas can lid fits Sears Allstate tank.
A Sears Allstate gas cap fits Blitz gas can.
The 1956-65 Allstate Mo-Ped tank has bottle-cap type threads, not machine-type. The inside of the gas tank neck is 34.4. The thread diameter is 44.6. Each thread is 4.0 mm wide.
The 1961-66 Allstate Compact scooter also has this gas cap, as do most late-50’s and 60’s Puch mopeds and scooters.
1981 Medallion
’80 Columbia Medallion
The 1980-81 Columbia Medallion (top tank model) has a molded plastic tank like a gas can. The thread diameter is 54.7 mm (2.16 inch), for a 55 mm bottle-cap type screw-on gas lid.
18. Pop-up gas caps
18a pop-up clamp-on
for 45mm OD tank $28
Pacer Sport (Italtelai)
Baretta 22,44 (Piccoli)
Westwind (Spisni Lino)
Negrini Harvard
18b pop-up locking chrome
for General, Lazer top tank
with 2 keys, none available
18b keys 719 and 459 (copy) $7 each
19. Information and Explanation
More gas caps, not for sale, for your information:
60. screw-on 40mm
very coarse thread
for modern ATV
61. screw-on 50mm
very coarse thread
for modern ATV
62. screw-on 50mm
very coarse thread
for modern ATV
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.
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, 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.