Compasses again.

Does anyone have an early 1940 UKicon Mk3, TG Co Ltd made prismatic compass. These early 1940’s dated differ from the usual later Mk3’s in that the inner bowl, the liquid container sealing glass is clamped down and sealed by a 1.5” diameter x3/32 deep x 1/8”wide externally threaded brass ring. The externally screwed down ring is screwed using a pin spanner in the two opposite 3/64” holes. Another visible sign is that the bowl is filled from the top at the 9o'clock position but UNDER the rotating index ring, via a 4BA red painted filler sealed with a fibre washer and most definitely covered with shellac varnish! Apart from that, they are pretty well identical to the later bog standard Mk3 prismatics.

In fact, until you lift the lid, it’s nigh-on impossible to tell the difference between the early ‘screw-down’ clamping ring top fillers and the later 8x screw, ‘screwed down’ clamping ring side fillers. All 3 eminently serviceable early obsolescent Mk3’s that I found on the shelf had been fitted with the top screen guard which made identifying them externally doubly difficult. I thought all of the early ‘top fillers’ had been replaced ages ago!

I asked the Instrument Shop supervisor what spares were still available and it appears that they’re all pretty interchangeable – even the complete bowl as an assembly! Looking at some of the other standard early ones, it seems as though they’d probably started out their life with early screw-down/top filler bowls too. As for early bowl spares, then only the 1/32" thick x 1.5" dia. O-ring glass seal and the 4BA fibre filler plug washer are still available but then, only at Base Workshop level.

Anyone out there got one of these early compasses?
Information
Warning: This is a relatively older thread
This discussion is older than 360 days. Some information contained in it may no longer be current.