Pool Cue Joints Explained 2026: 5/16×18, 3/8×10, Uni-Loc, and Radial Pin Compared

If you have ever tried to swap a shaft from one pool cue to another and discovered that the threads don’t fit, you have already met the world of cue joints. The joint — the metal or composite connection where the butt and shaft meet — is one of the most important specs on a pool cue, and it is also the spec most newer players ignore until it bites them.

This guide breaks down the four joint systems you will see on virtually every modern pool cue: 5/16×18, 3/8×10, Uni-Loc, and Radial. Knowing which one your cue uses determines what shafts you can swap onto it, what extensions fit, and what you should look for the next time you upgrade.

Why the Joint Matters More Than You Think

The joint is doing two jobs at the same time. Mechanically, it has to lock the shaft and butt into a single rigid unit so the cue plays as one piece. Acoustically, it transmits vibration from the tip back through the cue — which is where the “feel” and “feedback” of a cue comes from.

Different joints transmit different amounts of vibration. A flat-faced wood-to-wood joint feels different from a piloted brass joint. A modern carbon-fiber Uni-Loc style joint feels different again. None of them are objectively better, but if you have ever played with a cue that “feels dead” or “feels too lively,” your joint is part of why.

Just as importantly, the joint determines compatibility. If you have a 5/16×18 butt, a 3/8×10 shaft will not screw onto it. Period. Buying a shaft online and discovering this after the fact is one of the most common pool-shopping mistakes.

The Four Joint Types You Need to Know

5/16×18 — The Standard American Joint

The 5/16×18 joint is exactly what its name says: a 5/16-inch diameter pin with 18 threads per inch. It is the legacy American production joint, used on the vast majority of mid-priced playing cues, including many Quarter King production cues, Players, Lucasi entry-level, McDermott Star, Viking standard, and many others.

What you get with 5/16×18:

• Wide compatibility. Most aftermarket shafts are available in a 5/16×18 option
• Affordable shafts. Replacement maple and entry-level low-deflection shafts are easy to find
• A more traditional, “heavier” feel. The longer, coarser-threaded pin transmits less direct shaft vibration than newer fast-thread joints

If your cue is a production-line American playing cue from the last 30 years, there is a strong chance the joint is 5/16×18. Check the box, the manufacturer’s spec sheet, or simply unscrew the shaft and look at the pin — 5/16×18 has visibly coarser threads than 3/8×10.

3/8×10 — The Custom and High-End Joint

The 3/8×10 joint uses a thicker pin (3/8 inch) with much coarser threads (10 per inch). It is the dominant joint on custom cues, higher-end production cues, and many cuemakers’ shop standards. You will see it on Schon, Viking custom, McDermott G-Series, many Lucasi Custom builds, and most independent cuemakers.

Strengths of 3/8×10:

• Faster screw-together. Coarser threads mean the cue assembles in fewer turns — small thing, but noticeable in a long session
• Stiffer, more direct hit. The thicker pin and reduced thread engagement transmit more energy from shaft to butt, producing what most players describe as a “crisper” hit
• Common on custom cues. If you are buying a custom-built playing cue, 3/8×10 is by far the most likely spec

3/8×10 is generally not cross-compatible with 5/16×18 cues, although adapter pins exist for some applications. If you own a 3/8×10 butt, you must buy a 3/8×10 shaft.

Uni-Loc — The Quick-Release Modern Standard

Uni-Loc is a proprietary quick-release joint developed by Predator and now licensed across many cue manufacturers, including Cuetec, Mezz, McDermott, and many others. Instead of multiple full turns, a Uni-Loc joint engages and locks in roughly a half turn.

What makes Uni-Loc distinctive:

• Half-turn assembly. Faster and more convenient than threaded joints, especially in tournament settings or when you switch between break and playing cues frequently
• Consistent torque. The locking mechanism applies a consistent clamp pressure every time, which improves shot-to-shot consistency
• Tight integration with low-deflection shafts. Most carbon fiber shafts (including the Predator REVO and Cuetec Cynergy lines) are built primarily around Uni-Loc

If your cue is a modern Predator, Cuetec, Mezz, or carbon-fiber-equipped McDermott, you almost certainly have Uni-Loc. The joint face is recognizable: the shaft side has a brass insert with a slotted recess instead of a long threaded pin.

Our 2026 carbon fiber shaft buyer’s guide covers the major Uni-Loc-compatible options across price points.

Radial Pin — The Flat-Faced Specialty Joint

The Radial Pin is a precision-machined, multi-thread joint developed by Predator originally and now used on many high-end carbon fiber and custom cues. Where Uni-Loc is built for speed, Radial is built for precision and a flat-faced, wood-to-wood feel.

Key attributes:

• Flat-faced wood-to-wood contact. Many players prefer the more “traditional” feel that Radial provides over the slight metallic damping of other joint types
• High precision. The radial cut threads engage extremely tightly, producing a very stiff, repeatable connection
• Common on Predator high-end and custom builds. If you have a Predator Throne, Sport II, or Cynergy Series cue with the Radial option, this is what you have

Radial-pin cues often have shaft options that include Predator REVO and Vantage carbon fiber, plus traditional maple. They are not cross-compatible with Uni-Loc shafts despite both being Predator-developed.

How to Identify Your Cue’s Joint

If you do not know what joint your cue uses, here is the diagnostic:

1. Unscrew the shaft. Look at the pin sticking out of the butt
2. Long, slim pin with fine threads — likely 5/16×18
3. Thicker pin with coarse, widely-spaced threads — likely 3/8×10
4. Short pin with a threaded tip and a smooth shaft section — likely Uni-Loc
5. Flat brass face with a recessed pin and visible “spokes” — likely Radial

If you are still unsure, photograph the joint and contact your cue’s manufacturer. They will identify it from a photo in seconds.

What This Means for Buying Shafts

Joint compatibility is non-negotiable. When you are shopping for an upgraded shaft, the listing must explicitly say it is available in your joint type. Most reputable retailers, including Quarter King Billiards, list the joint on the product page; if it is not listed, ask before you buy.

For most production playing cues, the most common upgrade path is from a stock maple shaft to a low-deflection or carbon fiber shaft in the same joint. The Quarter King Carbon Fiber Shaft ($269.99) ships in 5/16×18, 3/8×10, and Uni-Loc options. The Predator REVO 12.4mm covers both Uni-Loc and Radial. The Rhino Carbon Fiber Shaft ($199) is Uni-Loc only.

Joint Type and Hit Feel

Players often ask which joint type “plays best.” The honest answer is that the joint is one variable in a much bigger system that includes shaft material, ferrule, tip, and balance — and the differences between joint types are real but smaller than most people assume.

That said, broad generalizations:

• 5/16×18 tends to feel slightly softer and more traditional
• 3/8×10 tends to feel firmer and more direct
• Uni-Loc feels modern and consistent — designed around carbon fiber shafts
• Radial tends to feel flat, stiff, and precise

If you are upgrading your playing cue, the joint type generally follows from the cue’s brand and shaft generation. You do not usually shop for a joint type — you shop for a cue, and the joint is what comes with it.

Joint FAQ

Can I use a 5/16×18 shaft on a 3/8×10 butt?

No. The threads do not match. Using the wrong shaft can damage the threads on either the butt or shaft.

Are joint protectors universal?

No. Joint protectors thread onto the same pin your shaft uses, so a 5/16×18 protector only fits a 5/16×18 cue. When buying joint protectors, match them to your cue’s joint type.

Is Uni-Loc better than 5/16×18?

It is faster to assemble and pairs more naturally with carbon fiber shafts. Whether it “plays better” comes down to feel preference. Many top professionals play 3/8×10 and 5/16×18 cues at the highest level.

Can I change my cue’s joint type?

Technically yes, with a custom rebuild by a cuemaker. Practically, the cost almost always exceeds the price of buying a new cue with the joint you want.

Bottom Line

Pick a cue you like, then build your shaft and accessory choices around its joint. Most players never need to think about this past the initial purchase — but the ones who do shop without checking are also the ones returning shafts that won’t screw on. Save yourself the round trip.

If you are still in the process of choosing a cue, our guide to buying your first pool cue covers the big decisions before you get to joint specifics.