Review on Z Threaded Hex Flanged M8 1 25 Internal by Paul Williams

The 3/8 inch (9.5mm) pilot hole was close enough. I "tapped" the hole with a 3/8 screw to be sure. increasingly when he wanted to sit down. I recommend countersinking/countersinking the hole to allow the wood to rest directly on the roller track/mounting plate and then tightening with channel locks. Otherwise, the shank is the only part that will withstand side loads and thread engagement will not begin until after the hex wrench is removed.