Milwaukee 1/4 in. - 1-3/8 in. #5 Black Oxide Step Drill Bit (10-Steps) 48-89-9205 - The Home Depot
1/8”-1-3/8” Step Drill Bits with Center Punch
Drill Bit Set 8 PCS Metal Drill Bits for Wood Impact Driver Steel Dril – SATC
Amazon.com: SILATU Step Drill Bit - 1/4” to 1-3/8” Step Drill Bits for Metal, High Speed Steel Black Coated Stepping Bit, Unibit Ten-Flute Step Drill Bit Sizes for Wood, Metal, Plastic, Multiple