For a lag screw, the pilot hole should be how in relation to the lag diameter?

• A. Slightly larger (more than lag diameter)
• B. Equal in size
• C. Slightly smaller (1/16 - 1/8 inch)
• D. Much larger

Answer: (C)

For a lag screw, the pilot hole should be slightly smaller than the screw’s outer thread diameter. This undersize lets the threads cut into the wood and bite, creating a tight grip that resists pulling out. A gap of about 1/16 to 1/8 inch is typical; it provides enough wood engagement for strength without causing the wood to crack or making driving excessively hard. If the hole is too large, the screw won’t engage enough wood and holding power drops; if it’s too small, driving becomes difficult and wood can split. This undersized pilot hole balances ease of installation with strong withdrawal resistance.