IIRC (which is always in question these days) the short filter used a spring and the long one didn't. That's 60+ year old memory for ya.
That's the way I remember it too. I'll have to ask my retired mechanic cousin next time I talk to him....
I also remember there being 2 different styles of the nut/filter housing that screw into the carb body. IIRC the Chevy/GMC carbs had the fuel line come in from the passenger side of the engine (up from the fuel pump) and
most of them had the shorter nut and the short filter. Some had the long one, and there's also a brass "rock" filter(AC#GF455) that fits like the short one. May predate the square body carbs though, but has better filtration.
The Pontiac/Buick/Olds/Caddy carbs had the line come more from the front (different fuel pump location on some) and that straighter connection has the longer filter.
This is my recollection from the parts store in the 70s and 80s, and helping Dad with the QJs on our vehicles. Last time we had one apart was prolly 20 years ago....
Maybe it has already been mentioned, but the spring helps to hold the short filter in place, so it does its job. Whoever designed this was a genius, except for having to change the filter and get the nut threaded in properly, and then threading the fuel line in and not messing the whole thing up. What Dad did on our rigs was install the AC #GF62C auxiliary filter, that has a metal can that threads onto an aluminum adapter that bolts to the frame inline with the fuel line from the tank. Under the cab is a good place on a pickup, under the second row door on a Burb. This uses an AC # GF157 filter cartridge that's about the size of a soda can, and that way you don't have to mess with the little one very much. I think we got a year or more out of those cartridges, even driving every day.
GM got smart on the injected trucks, with an inline filter that's easy to access on the frame. Even has a bracket that holds it and the lines....
