Allgrip Cup Square -555 M8 x 45mm, Hex, BZP, supplied in a pack of 200.
Cup square bolts have a smooth domed head with a square shoulder that bites into timber as the nut is tightened, so the bolt cannot spin. Used for gates, fencing, decking frames, sleepers and any timber-to-timber or timber-to-steel joint where the head must sit flush and cannot be reached with a spanner.
Pre-drill a clearance hole, insert the bolt and tighten from the nut side with a spanner or socket.