Product Overview - AM02-TAB - Tackform, Semi Truck Tablet Mount - Bolt On Install Kit. 

HI Trish! So sorry for the delay. A 7/32" drill bit would work best but you can also go the next size up. But don't go over 1/4"

@@TackForm Thank you! I figured it out and took the same advice from another commenter on your other Tackform video. The mount is rock solid.