600 Domi 99 Clutch Centre Nut

You need a narrow walled socket, or grind one down a little - I can’t remember the size but it isn’t metric!  I made a clutch locking tool by welding two plates together and adding a handle.

 RGM says its 5/8 x20TPI https://www.rgmnorton.co.uk/buy/clutch-location-nut-all-models_497.htm

…I used a 1/2”W box spanner with the external hex points relieved a little on the grinder to clear the internal threads on the clutch centre.

It’s double ended so the external hex on the other end (7/16W) fits a socket for loosening and tightening purposes.

Hope this helps.

Edited because I got the ends the wrong way round first time!

Available at online tool shops from a little over £5 and Amazon from a little over £6.

One of my first tasks, as an apprentice, was to make my own tools. This included box spanners and puller / extractor.  The box spanner was simply a short length of thin walled tube heated to cherry red and placed over my clutch mainshaft nut. As it cooled it gripped the nut at which point I bashed in the sides to match the nut flats. Still using it 50 years on.

I made a second one for a friend but only thicker water pipe tubing was available. No problems as,  after repeating the above process, the tube end was ground down until it would slide inside the clutch spider centre. 

The puller / extractor just happed to fit the engine spocket on my Dominator. That is still around as well.