A: ABEC (US) maps to ISO P grades; higher numbers mean tighter tolerance and higher speed limit: ABEC-1 ≈ P0 (general), ABEC-3 ≈ P6, ABEC-5 ≈ P5, ABEC-7 ≈ P4. Export bearings are often marked P0/P6/P5. P0 suffices for general industry; P5/P4 serve machine-tool spindles and precision instruments. Higher precision is not the same as longer life—size by speed and duty.