Discussion in 'Engineers' Talk' started by fred812, Jan 13, 2022.
How do I specify and buy these?
Think the socket is 1.5mm Hex but burred so hard to be sure.
Thread looking too coarse for metric so might be 1/8 rather than metric, what are they from?
It's the grub screw that holds the ceiling rose of a light onto the bracket that's fixed to the ceiling.
Measure the pitch as accurately as you can (put the screws side by side with one thread or so engaged to get more length, on your steel rule, measure the length of the threads over a convenient number of thread crests, work out threads per mm and also convert to threads per inch), measure the diameter of the threads across the thread crests of one screw ("major diameter", using vernier calipers or micrometer), look up the thread on https://www.fastenerdata.co.uk/thread-chart or similar.
It looks to me as though you've got, very approximately, 4 threads in 2mm, i.e. pitch is 0.5mm, which would make it M3 ISO coarse, and the major diameter may be about 3mm, but it's hard to be exact from your photo.It could also be some Imperial or American thread, but precise measurements needed, refer to chart.
Plenty of places sell them - jusrt depends on where you are.
Even SF stock them https://www.screwfix.com/p/easydrive-grub-screw-selection-case-350-pcs/7887j
To me, the pitch looks like 0.6mm but diameter is only 3.0 or 3.2 mm
TRy it against an electrical back box screw - they are 3.5 x 0.6 so that will check the pitch and see how diameters compare.
Ok, many thanks for the advice.
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