This is a crank shim to fit between the crank and drive bearing.
It will space the crank away from the drive oil seal plate.
It can also space up the layshaft if fit between the layshaft and bearing to tighten the main gear shim.
Size 0.8 - 1.5mm 25mm ID 1.5mm
You can replace the drive plate to a MRB one MBP0085