Spider gas caps: interchangeable or unique?

[Austin]

In preparation for moving the 68 Spider, I'm trying to sort out a few specific things. Already have new tires in place and noticed that it has an apparently home made gas cap.

Found a period locking gas cap meant for a 124 Spider but no mention of its size or whether it would work for an 850, though some other parts listing mention them being interchangeable.

Can anyone comment on whether a locking gas cap meant for a 124 Spider could be used for an 850 Spider?

 

[NM850]

Probably not. The early spiders had tabs and later ones are threaded.
In any case the spider gas caps are stylized and a locking cap would not look original.

 

[Austin]

Understood, thanks for input. Not as concerned about aesthetics as I am about getting a decent seal on the tank.

 

[Ulix]

Early X1/9s had the same chrome cap as the 850.
Modern Fiat caps from the 80s also fit the X.
So I would think that the threads are pretty universal.
FWIW.

 

[Jeff Stich]

Early X1/9s had the same chrome cap as the 850.
Modern Fiat caps from the 80s also fit the X.
So I would think that the threads are pretty universal.
FWIW.

The early X1/9 used the same threaded cap as the late 850 Spider, but the early 850 Spiders used a 1/4-turn (non-threaded) fitting on the fuel tank neck, thus the internals (bottom) of the early cap are different than all the other Fiats (as pointed out by NM850). Both caps have the same 3-eared chrome top, but different internals.

Being a '68, Austin's 850 would have the early 1/4-turn tank/cap combo, not threaded like an X1/9 or 124 tank/cap. Unless, of course, a previous owner replaced the tank with one from a 1970-73 850 Spider, which would have the threaded tank neck/cap combo.