Quick Answer / Summary: Most 4 mm panel jacks need a hole matched to their threaded body, commonly around 8 mm, with a shoulder that seats on the panel face. Drill a pilot first, support the panel from behind, keep at least one hole diameter of material from any edge, and de-burr both sides before fitting the jack.
A panel jack needs one hole, and the hole is where most home-built panels fail. It is either too large, so the jack rotates, or too close to an edge, so the panel cracks when the plug is inserted.
Sizing the Hole to the Jack
Panel jacks are specified by body diameter, thread and the diameter of the shoulder that sits on the panel’s face. The hole must clear the body but be smaller than the shoulder, or the jack pulls through. Where a jack is supplied with a nut and washer, the washer’s diameter is the practical limit for the hole.
Measure the Thread, Not the Body
The threaded section is what passes through the panel. Measure across the threads with calipers, then choose a drill slightly larger so the thread does not bind and chip the panel’s coating.
Insulating Bushes
On metal panels, the insulating bush occupies part of the hole. Its outer diameter, not the jack body, sets the drill size, and forgetting it produces a hole too small for the insulation.
Drilling Without Damage
A pilot hole locates the cut and stops a large bit wandering. Support the panel with a backing block so the bit does not tear the exit face, and reduce pressure as the tip breaks through. Plastics crack when the bit grabs, which a pilot and a slow speed prevent.
Edge Distance
A jack inserted and removed repeatedly applies leverage to the panel. Keeping at least one hole diameter of material between the hole edge and any panel edge or another hole prevents the classic crack that runs from the hole to the corner.
De-Burring and Flatness
Burrs stop the jack seating flat, which tilts the shroud and makes insertion feel tight. De-burr both faces, then check the jack sits flush before tightening its nut.
Correcting an Oversized Hole
A washer on each face spreads the clamping load and restores a firm fixing. Where the hole is far too large, a reducing bush or a jack with a larger shoulder is the cleaner repair than a stack of washers.
Hole Sizing Guide
| Item | Typical Figure | Check |
|---|---|---|
| Body diameter | About 8 mm | Caliper across thread |
| Shoulder diameter | About 12 mm | Must exceed hole |
| Pilot hole | 3 mm | Locates the main cut |
| Edge distance | One hole diameter | Prevents cracking |
| Washer | Fitted under nut | Distributes load |
Practical Applications
Building a patch panel, replacing a jack in an existing hole, mounting sockets in an enclosure, and correcting a hole that was drilled too large.
Frequently Asked Questions
What size hole does a banana jack need?
Commonly around 8 mm for the threaded body, with a shoulder of about 12 mm that must be larger than the hole. Measure the specific jack and any insulating bush before drilling.
Why did my panel crack around the jack?
Usually too little material between the hole and the panel edge, combined with the leverage of inserting a plug. Keep at least one hole diameter of material and support the panel while drilling.
How do I fix a hole that is too large?
Fit a washer larger than the hole on both faces, or move to a jack with a bigger shoulder. Enlarging further and using a reducing bush is the alternative.