10mm "pilot" hole. U-drill ;~')) Good for your barrel lenses and custom sizes. Very nice quality. Don't know who made 'em but most likely China I'm sure. $12 + $5 for the mailman. The more you buy the cheaper they get. Shipping one time. Get 10 for same shipping as for a single or multiples. Price ea. drops with multiples. Have over 10 right now.