I just had a look in the parts book for the E10 Cherry,wich came with A10 and A12 engines.The A10 pistons were 12010-18021 till 05/72,then 12010-H2301.The A12 piston was 12010-H1011.It seems that they first used the B10 piston,then for some reason the number was changed.No idea if there was a change on the piston itself,I never had the opportunity to open a B10 engine and compare.As Dodgeman said the dimensions are identical,and it is an easy swap to gain some compression on an A12.Datsun SSS,are these the pistons from that rallycross engine and are they standard bore?Any pics and info on the rest of that engine?I am still interested to learn more about it as that car was prepared here in Belgium.I haven't found any info about it yet,but I keep asking around.....