Custom ferrules for seat-belt harnesses

AN4 bolts are used to secure the seat belt harnesses. However these harnesses have 10mm holes. So even if one accepts the slop, the AN960 washers only provide about 1.2mm margin for retention and only if they somehow remain centered.

I have eliminated the slop by machining ferrules from AN4 washers. Starting with a number of AN960-4 (1/16") and AN960-4L (1/32") washers clamped on a AN4 bolt, over a thin layer of tape to better centre the washers, I ground the diameter down from 12.5mm down to 10mm, then finished off with progressively finer grit sandpaper. The result was impressive.

I have improved the retention by enclosing the seat belt harness between two AN970 washers, which have a much greater diameter. I used AN970-3 washers and reamed the centre hole to 1/4" rather than use AN970-4 washers as the latter were unnecessarily large.

Now having machined both normal 1/16" and thin 1/32" washers I can stack two of the first type to make a spacer which holds the AN970 washers 1/8" = 3.2mm apart. This scheme accurately centres the 2.5mm thick seat belt harness but allows it to rotate freely. Alternatively stacking one machined washer of each type to hold the AN970 washers 3/32" = 2.38mm apart when tightened I can both centre and rigidly clamp the seat belt harness. I am currently undecided what scheme I should use on the side harness connections, but it is clear I should use the free-rotating connection for the rear harness connection at the bulkhead wall.