20 Hex socket (M8 20). More Usage and Install: pre-drill a proper hole, screw-in with Screws Threaded Inserts. 15 Hex socket (M6 10). 20 Hex socket (M6 15). 30 Hex socket (M5 10). Features of insert nut: These threaded inserts are inserted into a pre-drilled hole by screwing in, in that case the external protrusions bite into the wood, preventing the nut from either turning or pulling out.
eBay