Description
The problem shows up on the jobsite, not in the yard: a rig with a 5/8″-11 spindle and a box of bits cut for 1-1/4″-7. Two different thread standards exist in North American core drilling and neither is going away, so at some point every crew needs the adapter.
Which thread is which
As a rough guide, 5/8″-11 is the handheld standard — small dry bits, angle-grinder-style tooling, light handheld drills. 1-1/4″-7 is the rig standard, used on stand-mounted and larger motors where torque and barrel diameter both go up. Bits from either family will not thread onto the other machine, and forcing a mismatched thread will strip one or the other.
What this adapter does
It converts a 5/8″-11 male spindle to accept a 1-1/4″-7 female bit, which is the direction crews normally need: putting a larger rig bit onto a smaller handheld machine for a one-off hole. Machined from solid steel with the hex flats needed to break the joint after drilling.
Two practical notes. Fit a copper washer or a smear of grease on the shoulder or the bit will seize onto the adapter after a long wet cut. And check the motor is rated for the bit diameter before you fit one — an adapter lets you mount a bit your machine may not have the torque to turn. Both standards are set out side by side in our thread and sizing guide. More hardware under core bit accessories.
