just under 1/8" diameter. perhaps part of a seal? bike is running good, the only leak I've got these days is the oil pressure sender and I just installed a new crush washer so that should be GTG. I did just pull the top end & cylinders off to re-seal over the winter- though I don't recall anything that looked like the pieces in question . they're hard brittle plastic bits. I cut the oil filter open as well- nothing weird in there. I have a spare pan gasket- I'll yank the pan if you guys can tell me what to look for otherwise I'm just gonna keep running this old tractor engine. I did do a quick boroscope inspection through the oil drain hole- saw no more plastic bits.