Can anyone identify this 1975 Yamaha DT 100 piston as being standard or over sized
What rings would be needed
Thanks

Happy to be corrected here, but my understanding is that genuine Yamaha oversize pistons have the oversize stamped on them - eg 0.25, 0.5 etc. I couldn't see anything like that in your photo, so my best guess would be that it is standard size.

Ok, my guess is it's 1mm oversize at 53mm as says 53 on top [52 std] so 4th oversize in yamaha speak. BUT--measure it to be sure. As above with Gr8uncleal i was thinking Std size except yamaha always have numbers like 98 97 something like that which i think is incremental's of a tighter Std fit--like highest number would be the tightest Std fit on a new cylinder. As usual i could be wrong lol.

Picture of underside and side and pictures of rings would be helpful...

Often there is some sort of manufacturer name underneath inside.