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Where can I get this? About 100mm long or longer? Its basiclly a set screw, but needs to be min 100mm? Like this, deosnt need the dog end, just and allen hex head sunk into it. I can#t find any longer than 60mm in m8.

If you have a drill, buy a length of threaded rod from B&Q or such, drill a 4mm hole in the end and epoxy an M4 allen screw into it? Or if you have the tools, drill and tap then epoxy.
Correctly known as a stud. Not always with the hex socket, but you should be able to find some:
https://www.toolstation.com/shop/p70719?r=googleshopping&rr=marin&utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&gclid=Cj0KCQiArqPgBRCRARIsAPwlHoUgcHslPucyck9u3NjGtt81MNzw5o07agdVk9yKjqEStNi-KSUukJIaAjQWEALw_wcB

Correctly known as a stud.
My reputation precedes me
Worth looking closely at any 'Studs' through - as the ones intended to use as a resin-fixed anchor often have the end cut at a bevel or point
Both good finds, perfect cheers.