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Machining Terminal Plates and Binding Posts for Speakers

September 17, 2026

A terminal plate is a small part that gets handled harder than anything else on a loudspeaker. People tighten it with their fingers, with pliers and occasionally with a spanner, and they do it years after the product left the factory.

Binding post spacing

Start here, because it constrains the whole plate.

19.05 mm (0.75 in) centre to centre is the standard, set by the moulded dual banana plug. Use it unless you have a deliberate reason not to.

Consequences of that number:

• Two posts at 19.05 mm centres need bodies that fit inside that pitch, including their insulating shoulders. Check the post’s maximum body diameter, not just the hole.
• A four post plate for biwiring is two pairs, each at 19.05 mm internally, with a larger gap between pairs so the pairs are visually distinct and a spade on one does not touch the next.
• Leave room for a spade connector to sit flat and for a banana plug’s body, which is wider than the pin.

The plate

Property	Typical	Why
Material	Aluminum 6061, or brass, or ABS/POM	Metal for appearance and stiffness, plastic where isolation matters
Thickness	3 to 6 mm in metal	Thick enough that the post nut does not deform it
Hole diameter	8 mm typical, 10 mm on heavy posts	Check the specific post
Anti-rotation	Flat, tab slot or D-hole	Matched to the post’s shoulder
Rear clearance	Room for the internal nut and a ring terminal	Usually forgotten until assembly

Two details that cause warranty problems:

1. Isolation. If the plate is metal, the posts must be insulated from it, or the two terminals are shorted together through the plate. Posts sold as insulated come with shoulder washers, and the hole size assumes they are fitted. Dimension the hole for the insulated assembly, not for the bare post.
2. Sealing. On a sealed cabinet the terminal plate is part of the enclosure. A leak at the plate or around a post changes the alignment of the bass. The plate needs a gasket or a sealant landing, and the post needs to seal at its shoulder.

Anti-rotation, in detail

This is the single most common failure on a machined terminal plate.

The post has a shoulder with a flat, a square, a D or a small tab. The plate needs the matching relief. If the plate just has a round hole, the post is held by friction from the nut alone.

What happens then: an owner connects a spade and tightens it hard. The post rotates. The internal wire, which is soldered or crimped to the back of the post, twists. Repeat over a few years and it work hardens and breaks, usually on one channel, usually out of warranty.

On the drawing:

• Show the anti-rotation feature dimensioned, with its angular orientation relative to the plate
• Give it a snug fit, not a loose one, because a loose D-hole allows a few degrees of movement which is enough to twist wire over time
• State the orientation you want the flats to end up in, because it affects how the internal wiring is dressed

Plating and contact resistance

The current path is the post, the nut, the wire and the connector. Every interface in that path has a contact resistance that rises as the surfaces oxidise.

• Nickel plated brass is the workhorse. Hard, durable, a slight resistance penalty against bare copper that is irrelevant at loudspeaker impedances.
• Gold plated brass does not oxidise at the contact surface, which is the real benefit. The plating is thin, so specify a nickel underlayer or the gold migrates into the brass over time.
• Bare brass or copper looks superb on day one and dulls within weeks. Contact resistance rises as it does.
• Rhodium for high end. Hard, bright, expensive.

Specify the plating with an underlayer and a thickness, the same way you would any finish:

FINISH: ELECTROLESS NICKEL 5-8 MICRONS,
THEN GOLD 0.2-0.5 MICRONS OVER THE CONTACT AREA
MASK THE THREAD

That last line matters. Plating builds up in a thread and a plated thread can bind.

Cosmetic requirements

A terminal plate is on the back, which tempts people to treat it as non-cosmetic. On high end product it is photographed, and buyers look at it in reviews.

Practical position: treat the plate face as a secondary cosmetic zone. No tool marks, uniform finish, clean engraving for the polarity and channel markings, but you do not need the front panel’s standard. Say that explicitly on the drawing rather than leaving the shop to guess, per the cosmetic zone scheme.

Polarity markings are a safety and usability requirement as well as a cosmetic one. Engraved and paint filled, or laser marked, both outlast a printed label.

Drawing checklist

• Post spacing at 19.05 mm unless deliberately otherwise
• Hole diameter for the insulated assembly, not the bare post
• Anti-rotation feature dimensioned and oriented
• Plate thickness adequate for the post nut torque
• Rear clearance for nut, washer and ring terminal
• Gasket or sealant landing if the cabinet is sealed
• Isolation from the plate confirmed if the plate is metal
• Plating with underlayer, thickness and thread masking
• Polarity and channel marking method
• Cosmetic zone stated

Frequently asked questions

Keep reading

• How a CNC Volume Knob Is Made and What Drives Its Price
• What a Turntable Platter Needs From the Shop That Machines It
• Machining Headphone Cups and Yokes That Match Left to Right

This guide is part of Knobs, Platters, Cups and Feet, one of four sections in the guide library.