From my experience, if you are going to thread then dense, fine grain is best. Noggin End have a good selection:

**LINK**

HTH,

Rod

Drop me a pm with your address & an idea of what size lump you need & I'll have a word with my MD. (I work for his graphite supply & machining company).

He has been amenable in the past to me raiding the oddments box for a suitable piece of fine grained isostatic graphite for this purpose. All that has been asked in return is that the recipent sends in a picture of the finished product.

He provides the graphite & I pay the postage – make a donation to charity if you would like, but not compulsory !

Nigel B.

Many vacuum cleaners pull the air through the motor so be sure that the very fine dust will stay in the bag and not get deposited in the motor, I doubt a one off job will cause a problem but if you use a lot of graphite then it might be worth checking the motor for any deposits.

Mike