For the fixing of lampholders with a 10mm threaded base fixing these 10mm Allthreads 20mm long and with a hollow centre to allow the flex to run up the middle.
Sold in singles
Thread pitch is 1.0mm, internal diameter is 6.5mm
Remember to leave about 6mm for the commection to the lampholder. As a tip, if you need to stop the lampholder for turning use a spot of super glue but only a very small amount in case you need to remove the lampholder agaim.