ok this is where i point out there is no such thing as 5/16 chain, chain size "Pitch" is expressed by the distance between the centre of 2 rivets in the chain, such as from smallest to largest 1/4, 3/8 low pro, .325, 3/8. .404 being the only sizes you are likely to find short of playing with big old saws from the 60's 70's or a mechanical harvester head and "GAUGE" being the thickness of thedrive link that runs in the guide bar. At a guess i would say the chains on your smaller saws are actually 3/8 low profile chain(which is sharpened with a 5/16 or 4mm file) . a side by side pic with the .325 would help alot. to swap chains you need all of the following to match, chain, bar (pitch& gauge for sprocket tipped bars and gauge for solid tip) and the clutch sprocket. if your lucky enough that your saw uses rim sprickets then it should be easy enough to get the riquired sprocket and swap it over if it doesnt which is more likely that not then you would need to get a whole clutch drum assy to suit the smaller chains.
hope that helps
