I used to have a 3/8" to 5/8"-11 shank adapter (not Stadea) that flexed on the shank when the bit was hooked. Since my drill bit has a 1/2" shank, I switched to a Stadea 1/2" shank, which allowed me to slowly but surely drill a 14" diameter hole with an 8 amp drill bit. x 2 1/2" to drill into concrete. .