US manufacturers measure overbores in inches - .010", .020", .030", etc.

Import overbores are usually in metric dimensions (mm) and are sized as .25mm, .50mm, .75mm, 1.0mm, etc.

.25mm = .0098" (about .010")
.50mm = .0197" (about .020")
.75mm = .0295" (about .030")
1.0mm = .0394" (about .040")

Unfortunately, "about" is not a good way to measure overbores - so:

If you want a .030" overbore, you need to look for a .75mm oversized piston. They used to be available from Mitsubishi - not sure now. Custom piston makers can make whatever you want for about $600/set.

Be very careful that you (or better yet, your machinist) decide in metric equivalent what overbore size you need - and be very careful that you have the pistons in hand to give to the machinist before he bores your block.

Any rebore done the right way will have the pistons in the machinist's hands so he can measure them to see how much more he needs to allow for piston clearance.

Frank