Max Knives MKRB912 — 12 mm ball bearing, nine balls, 6 mm bore

Overview

The MKRB912 tops out the series. With a 12 mm outer diameter, a 6 mm bore and a thickness of 4.5 mm, it targets the most generous pivots, those of large folders whose axis reaches 6 mm. Its nine balls and 2 grams put it close to the MKRB910, whose construction it repeats one size up. Like the others, it is sold individually as a workshop part.

Thickness, the third dimension to check

Outer diameter and bore are the two measurements everyone thinks of; thickness is the one that gets forgotten. Here it is 4.5 mm, half a millimetre more than the other three bearings in the series, all of which are 4 mm. That half millimetre has to come from somewhere: the depth of the recess, the space left between blade and liners, the thickness of the washers used in the build. On a knife you are rebuilding, take that dimension before buying, just like the other two.

Technical specifications

Ball bearing, reference MKRB912, sold individually. Outer diameter 12 mm, inner diameter 6 mm, thickness 4.5 mm. Nine balls. Weight 2 grams. A workshop part for rebuilding a folding knife or smoothing its opening action. It is the only bearing in the series to reach 4.5 mm in thickness, the other three staying at 4 mm.

Care

Fit it into a dusted recess on a clean pivot, with a drop of fine oil to start the rotation. A bearing this size often sits in a knife that works for a living: the pivot then deserves a periodic check, if only to make sure the screw has not backed off. A rinse followed by thorough drying before re-oiling keeps the races clean.