I know little about M20s...probably best to keep it that way too...but the thread relating to fuel tank bosses is referring to 3/8" BSP fittings on the deLuxe tank. Is there an error or a reduction somewhere ?

You are right about that Rik. The adapter/filter #11 screwed into the tank boss is 3/8 BSP. That fitting was drilled and tapped to take an 1/8 BSP tap but later on was often changed to take a 1/4 BSP tap.

I just thought that the sizes mentioned were for the tap only?

Ron

email (option): ronpier@talk21.com

Ron, I said that I knew nothing. I've always been used to 1/4" BSP at both ends...always found it odd that BSAs had 1/8" taps as I imagined a tiny tank thread...I now understand that there is a reduction with filter. The filters on the 1/4" taps are a nuisance as with the slightest distortion, they catch on the threads and twist.

My M20 came at 'demob' with 3/8-1/4 BSP tank adapters and taps that were 1/4 x 1/4 BSP at both ends....So at some point REME were making the change...Ian

email (option): ian@wright52.plus.com

Thanks All, the thread is definitely different at both ends, I will try measure the thread and see how its drilled.
thanks
chris

email (option): cdpeach@hotmail.com

BSP(P) thread dimensions are as follows...1/8" BSP: O.D 0.383"...Threads per inch : 28. 1/4" BSP: O.D 0.518"...TPI 19. 3/8" BSP: O.D 0.656"...TPI 19...Ian

email (option): ian@wright52.plus.com