I don't know. Are these Kawasaki pistons? Do you have new piston ring sets? And do you have the Kawasaki factory service manual? I would think you're going to need a good caliper & need to do some measuring, and I would also think you could/should measure the pistons.
I looked up the KZ550-H1 GPz pistons on Partzilla & eebbaaay.
The 13027-1058 OS pistons have 100 stamped into the top of them.
The 13029-1062 OS pistons have 50 stamped into the top & one seller says it's the 1st oversize.
The 550 manual says there are 2 oversize pistons available, 0.50mm OS & 1.00 mm OS.
Regarding the numbers stamped into the tops: I would assume 50 = 0.50 mm OS & 100 = 1.00 mm OS.
For comparison, the KZ550-A3 pistons are stamped with 0.50 & 1.00, and the parts diagrams more clearly differentiate between the two.
The 13029-1055 piston has 0.50 stamped into the top & listed as PISTON-ENGINE L,O/S 0.50.
The 13027-1053 piston has 100 stamped into the top & listed as PISTON-ENGINE LL,O/S 1.00.
I assume L = 1st oversize (0.50 mm) & LL = 2nd oversive (1.0 mm).
1981 KZ650-CSR. Competition, Sports & Road.