Quick Answer

Choose the core bit diameter that is slightly larger than the pipe, cable or anchor it must fit. For pipes add a few mm of clearance; for electrical conduits use the conduit OD plus clearance; standard sizes run from 25 mm to 200 mm.

How to Pick the Diameter

Application	Typical Diameter
Electrical conduit	25–50 mm
Plumbing pipe	50–100 mm
Ventilation, large pipe	100–160 mm
Drainage, large openings	160–200 mm+

Key Rules

• Measure the outside diameter of what passes through the hole.
• Add 5–10 mm clearance for pipes; more for movement or insulation.
• Match the bit arbor/thread to your machine.
• Consider the core (plug) removal — larger bits need core-breaking tools.

How to Measure Correctly

1. Measure the pipe or fitting OD with a caliper.
2. Add clearance for fit, insulation, or thermal movement.
3. Select the next standard bit size at or above that total.
4. Verify depth needed to pass through the full wall thickness.

Frequently Asked Questions

Q: What is the most common core bit size?

A>For general work, 100 mm is very common; 50 mm and 68 mm are popular for pipes and conduits.

Q>Should the hole be bigger than the pipe?

A>Yes — add clearance so the pipe slides in and can be sealed properly.

Q: Can I use a smaller bit and enlarge the hole?

A:Not easily in concrete — enlarging destroys the bit and the hole. Start with the correct size.

Conclusion

Measure the fitting, add clearance, pick the standard size above it. Bits like the Continuous Threaded Tube Drill — JOY-CTT threaded tube and the Long Shank Hole Saw — JOY-LSH long shank cover a wide range of diameters for concrete and masonry.