Review on Z Threaded Hex Flanged M8 1 25 Internal by Sean Maile

The 3/8" (9.5mm) pilot hole was close enough. Insertion was light to moderate most of the time and increased as it wanted to sit down. I recommend countersinking/countersinking the hole to allow the wood to rest squarely on the roller track/mounting plate and then tightening with channel locks, otherwise the stock is the only part that will withstand side loads and it's just beginning to engage the threads after the hex key has been countersunk.