No. 72 vs No. 78 Drill Bits: Which Size for Your Project?
By Quality Tools & Supplies for Hobbys, DIY & Crafts - Micro-Mark Tools | Published: 2026-10-25
Category: Comparisons
Choosing between No. 72 and No. 78 micro drill bits? We compare the two sizes based on diameter, material compatibility, and precision to help you select the right bit for your model or craft project.
Quick answer
Choose No. 72 (.025 inch) for slightly larger pilot holes or dowel work, and No. 78 (.016 inch) for ultra-fine detail drilling in delicate model parts. Both are high-speed steel and work on wood, plastic, and metal.
Why diameter matters for micro drilling
When you're working on miniature projects—model trains, dollhouse furniture, or fine jewelry—the difference of a few thousandths of an inch can make or break a fit. A No. 72 bit creates a .025 inch hole, while a No. 78 bit cuts a .016 inch hole. That .009 inch gap is roughly the thickness of a sheet of paper, but it determines whether a 1/16 inch dowel slides in snugly or wobbles.
Material considerations for both sizes
Both bits are made from high-speed steel, which means they stay sharp longer than ordinary carbon steel bits. They can handle wood, plastic, and soft metals like brass or aluminum. For harder metals, you would need a cobalt or carbide bit, but for typical hobbyist materials, these HSS bits are a solid choice.
Trade-offs at a glance
- No. 78 (.016 inch): Best for ultra-fine detail work: drilling tiny holes for wire, pins, or micro-screws in soft wood, plastic, or thin metal. The smaller diameter reduces the risk of cracking fragile parts. If your project calls for a hole smaller than 1/64 inch, No. 78 is the right choice.
- No. 72 (.025 inch): Better for slightly larger pilot holes, such as those for 1/16 inch dowels or small screws. The diamond-grit edge helps it cut faster and stay sharp longer in harder materials. When you need a bit more bite and a hole that accommodates common small fasteners, go with No. 72.
- The trade-off: No. 78 gives you finer precision but requires a gentler touch and may clog faster in soft woods. No. 72 is more versatile for everyday hobby drilling but may be too large for the most delicate micro work.
Product facts at a glance
- No. 78 Drill Bits (Pkg. of 6): No. 78 drill bits have a .016 inch diameter and are precision-ground for accuracy and clean holes. This ultra-fine size is ideal for drilling tiny pilot holes in delicate model parts without splitting the material.
No. 78 Drill Bits (Pkg. of 6) - No. 72 Drill Bits (Pkg. of 6): No. 72 drill bits have a .025 inch diameter and feature fine diamond grit for quick, precise material removal. The slightly larger diameter and diamond grit make this bit more efficient for drilling in harder materials while still maintaining precision.
No. 72 Drill Bits (Pkg. of 6)
Which one fits your project?
Best for
- Model railroad detailers who need tiny holes for signal wires or rail joiners (No. 78)
- Dollhouse miniaturists drilling pilot holes for 1/16 inch dowels or tiny hinges (No. 72)
Not for
- Drilling into hardened steel or thick metal plates—consider carbide bits instead
