I've bought a couple of packets of 135mm long Fischer FUR universal
frame fixings from the local Screwfix for attaching the wooden
framework of my new workshop to the concrete block foundation. All's
well there, but I've got a minor problem when attaching the door frame
in that 135mm is too long and is in danger of going right through the
concrete block - horizontally. I really need one 120mm for this, for
which I really don't want to buy a packet.

Has anyone tried shortening one of these fixings and was it
successful? I could just try but I'm concerned about it not working
and having to dismantle rather a lot to sort it out.

Thanks
Rob