are all gas caps the same?

[mikey's250sx]

i have a tank but i don't know who makes it. i have read that yamaha caps fit ims tanks and that an ims cap will fit this tank. but i can't find an ims cap so i found a yamaha one. by my roundabout logic i should think it will fit. what do you think?

[oddball3]

Dennis kirk has the IMS cap. $11.99, but not sure if the yammi cap will fit.

[mikey's250sx]

didn't even think about the shops. i was thinking about ebay which is where i usually go for small stuff. got a front brake caliper for 2.25 plus shppg. service honda wants over 100 bucks for the same one.