Are there different chain widths and chainring spacings in the 5-8 speed chain range?
I've got an old crankset, an sr apex probably from the 5 speed freewheel era, and am using it with 6 and 7 speed freewheels and I think an "8 speed" chain. It shifts fine in the rear but sometimes when downshifting in front the chain rides between the rings. I'm looking to get a new chain and have seen most described as 6-8 speed or 5 speed, but some as 6-7 speed. I'm assuming the 5 speed chains would be thicker, maybe thicker than I want, but would there likely be a difference in width between the 6-7 speed and the 6-8 speed chains? Any measurement information or specific chain recommendations for my setup appreciated.

5 begat 6, same space , 7 thinned, 8 added at that space, after that things got thinner still..

this is such an FAQ, definitive measurements need a sticky on top in an obvious spot,
since no one looks back, first .

I can't really comment on chain rings, although steel rings are making a comeback! Why? Because thinner chains require thinner rings and so steel is still strong when thin.

As for chain widths:

9.0 - 9.5mm - single speed/BMX chains
7.4 - 7.6mm - 5/6 spd
7.1 - 7.4mm - 6/7/8 spd
6.6 - 6.9mm - 9spd
5.9 - 6.1mm - 10spd
5.5mm - 11spd

Thanks. Those sound like the outside measurements that I'm interested in and I haven't seen them. I need to get a pair of calipers and some old chains and try to figure out what's going on with the front shifting.

Thanks gyozadude!
Yet another tidbit I've now entered in to the record )
I vividly remember the SunTour Ultra 6 freewheel (still have one in fact)with it's narrower spacing for upgrading bikes with the 120 spacing to a 6cog. setup from the 5 cog.

I couldn't figure how to get a good chainring spacing measurement, but by comparing a few by holding them up against eachother (teeth to teeth with big ring to small ring of the other, if that makes sense) the sr apex did seem a little wider spaced than some other old cranks and a mid 90's campy record that was for an 8 speed bike, but just barely. I had an old shimano biopace crankset that was very noticeably narrower compared to all others, including an old shimano 600.
I measured the chain at 7.2mm, and I'm thinking a thicker chain, maybe a 5 speed chain, would probably help. I guess this isn't a common problem with older setups, and the sr apex less common still, but I'd still like to figure out chainring spacing and chainwidth changes better just out of curiousity.

Best way to fix this IMO is fit a big ring with lift pins.

The Sr Apex uses an obsolete bolt circle so it is a little harder to find replacements and if you do they are going to be Apex chain rings.

The old fashioned way to improve up shifts on non ramped rings was to gently bend a tooth inward just a small amount (not enough to affect smooth running of the chain) and one would do this at 3-4 evenly spaced points around the chain ring and then the teeth themselves serve as ramps / pickups.

Thanks, wouldn't have thought of that. Since I'm having problems on the downshifting, maybe bending out a few of the inner rings teeth would help. I was also thinking I could maybe put some bumps of jb weld or something on the inside of the outer ring to push the chain over onto the small ring better. It would be nice not to risk messing up the rear shifting with a thicker chain.

and narrower rollers , between the inner link plates,
require the thinner chainring teeth, and cassette cogs.
and the thinner metal in the inner link, is also the bushing edge the rollers ride on .

Cost more and wear faster .. the economics of "upgrading"..