Sirr0und Irwin 12" Extension Bit Double set screw with Allen wrench. Recommended for all 1/4" round shank drill bits requiring extra reach. Follows 5/8" and larger bits through hole. 1/4" shank. Only fits round shank Speedbor or Do it Best brand bits. MPN# 88601 SKU# 306289UPC# 24721886019