Front strut top mount sleeve nuts?

So I know what I need as I've seen them on Hackydan's, but can't seem to find them anywhere, and he hasn't answered    

With an omp strut bract fitted on top of the top mounts, the studs are too short and you can only just get the M8 nuts to lock on a few turns which doesn't fill me with confidence!

I've seen on a couple of UT's, what looked like allen head bolts rather than nuts, but on investigation realised they must be what I think are called 'sleeve nuts'?

The best match I can find are these on eBay, but I think they are more for furniture use as they don't look as heavy duty.

Anyone know what I'm talking about and where to get some?