Spacer E38 for Marui Samurai

the instruction manual of a Marui Samurai says that if you replace tenac bearings in the knuckles and rear arms by ball bearings, you should use the spacer E-38.

My samurai did not came with the unused parts from the build. I had to reinvent them (by deduction from the size of the ball bearing and the size of the tenac bearing used in the place before).