Ordering a piston

The piston I ordered is technically a piston for a BSA, however, it will work for my bike perfectly. I needed a +.020 piston (20 over the original production size piston) because as the piston goes up and down in the cylinder, it wares away the cylinder and makes the cylinder too big for the piston. The cylinder is made out of softer metal than the piston. Therefore, the piston stays the same size but it makes to cylinder smaller. They produce pistons that are slightly over production size just for this reason. I had to buy a larger piston because my cylinder is oversize. The +.020 fits snugly in my cylinder but finding an affordable piston that fit was a bit of a struggle. When one was found I bought it. The total for the new piston was $142 which includes shipping. This was the best deal for this size piston that we could find.