I've got a tatty mech, can just about make out 5SP3/32 on the very pitted outer cage. The chain link shows some wear and is a bit more flexible than I'd expect. I was keeping it in the vain hope that I might one day build a 1960s project but I really don't think that will happen. Prices being asked for similar or worse examples on Ebay are frankly ridiculous so if you're in the UK the whole thing is yours for £15 including postage.