GD normally weld a nut onto a M10 bolt (M10x1.5 thread), drill a hole through the centre, machine a flat surface and seal using a dowty washer.
I have decided instead of using the dowty washer, I will machine a 45 degree end on the bolt and use that as the seal, similar to a normal fitting.
It is taking me a little while to drill the hole through the centre of the bolt since I don't want to break the drill bit.
I started with a A4 stainless M10 x 55mm bolt, but probably could use a 50mm long one. To help grip it in the lathe chuck, I drilled out a M10 nut with a 10mm bit and slid it onto the bolt. The chuck then gripped the bolt head and the extra nut to help support the bolt.
I then faced off the bolt and centre drilled the end (this isn't quite centre for some reason!). I then used a 3mm drill bit to drill as far I could.
I then started turning down the end of the bolt to start making the 45 degree chamfer. I used the original belled nipple for size, and the turned down diameter is 7mm. This was done.
I then started on the 45 degree chamfer. I have now finished this end and have stared drilling in from the bolt head end. I managed to drill in around 15mm this morning before work, so hopefully can finish this of in the next day or two.