For the fixing of lampholders with a 10mm threaded base fixing these 10mm Allthreads 150mm 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
If you want to use this with braided cable, then you may need to run a 7mm drill bit inside the rod first to remove the seam mark.