Tool steel Ø 3 and 4 mm drill bits with assembled ring should be used with lower rpm than the recommended speed for the single drill bit
2599303 - Twist drill made of HSS
Easy back stroke of the power drill by spiral springs
BESSEY GM60Z-2K OMEGA screw clamp GMZ 600/120 2pc Plastic Handle
Also you can simply exchange the ball bearing guide Ø 9
FAMAG 7pcs TCT Bormax 3 Prima pilot Guided Forstner Carbide-tipped set, 1664570 Inspection Mirrors Tool steel Ø 3 andFAMAG 7pcs TCT Bormax 3 Prima pilot Guided Forstner Carbide tipped set, 1664570 7 pcs set in wooden case 15, 20, 25, 30, 35, 40, 50 mm. TCT Bormax prima with exchangeable centre point and pre drill bit. The two carbide tipped main cutting edges ensure a maximum service life also in hard and coated materials. Included in the delivery: Bormax, exchangeable centre point, pre drill bit 4 mm and one allen key. Hexagonal shank for a better power transfer.