Understanding the different sizes used in muzzle devices, tubes, and related components can be confusing at first. This guide breaks down the three most important measurement systems — Cell Size, Thread Protector Size, and Bore Size — so you can quickly identify what fits your firearm and what each dimension actually means.
Whether you are selecting a tube, checking thread compatibility, or comparing different designs, this page is designed to give you clear, practical information.
1. Cell Size Explained
Cell size refers to the outer diameter (OD) of the tube or main body. Different manufacturers use letter designations (A, B, C, D, etc.) as a simple way to describe the diameter class of the component.
Common Cell Size Chart
| Cell Designation | Approximate Outer Diameter (OD) | Typical Use |
|---|---|---|
| B Cell | 1.375″ | Very common industry standard size |
| C Cell | 1.250″ (approx.) | More compact designs |
| D Cell | 1.500″ | Larger internal volume |
What the Different Cell Sizes Mean in Practice
B Cell (1.375″ OD)
This is one of the most widely used sizes. Many modular systems, tubes, and accessories are built around the 1.375″ diameter. It offers a good balance between internal volume and overall bulk.
C Cell (approx. 1.250″ OD)
Slightly smaller than B Cell. These designs are more compact and can feel lighter, but they offer less internal volume.
D Cell (1.500″ OD)
Larger diameter tubes. They provide more internal space, which some users prefer for higher capacity or specific applications. The trade-off is increased size and weight.
Some manufacturers also offer additional sizes (sometimes labeled A Cell or other designations) for specialized or compact setups. Always check the actual measured outer diameter rather than relying only on the letter name, as naming conventions can vary slightly between brands.
2. Thread Protector Size & Compatible Calibers
Thread size is one of the most critical factors for compatibility. The two most common muzzle thread pitches in the United States are 1/2×28 and 5/8×24.
– 1/2×28 Thread Protector Compatible Calibers
Commonly compatible with:
| .22 | 9mm | 17HMR | 5.7×28 |
| 5.56 | .223 | .243 | .270 |
1/2×28 Thread: This is the standard thread for many smaller-caliber firearms, most AR-15 platform barrels use 1/2×28.
– 5/8×24 Thread Protector Compatible Calibers
Commonly compatible with:
| .308 | 45 ACP | .40 | 30-30 |
| 30-06 | 300 | 333 Lapua | 6.5 Grendal |
5/8×24 Thread: This larger thread is the standard for many bigger-bore rifles.
– 1.375×24 Thread
This is a common rear mounting thread used on many tubes and booster-style interfaces. It is not a muzzle thread on the barrel itself, but rather the thread found on the rear of certain modular tubes or adapters.
1.375×24 Thread: This thread size is for suppressors and solvent traps that require a booster assembly.
Important Notes on Thread Compatibility
- Always verify the exact thread pitch on your specific barrel. Manufacturer specifications can vary.
- Some European and specialty firearms use metric threads (for example M13.5×1 LH or M14×1).
- Never force a mismatched thread. Cross-threading can damage both the barrel and the device.
3. Suppressor Bore Size Explained
Bore size refers to the internal diameter of the opening that allows a projectile to pass through (when applicable). Choosing the correct bore size is important for safety and proper function.
Common Bore Size Categories
- .22 / Rimfire — Smaller opening designed for .22 LR and similar calibers
- 9mm — Suitable for 9mm and some similar pistol calibers
- 5.56 / .223 — Common for AR-15 platforms
- .30 Cal / 7.62 — Larger opening that can usually also safely handle smaller calibers
Key Considerations for Bore Size
- A larger bore can often safely handle smaller calibers, but the reverse is not true.
- Using a bore that is too small for the cartridge is dangerous.
- Some modular systems allow different end caps or inserts to change the effective bore size.
- Always match the bore to the largest caliber you intend to use.
How to Use This Size Guide in Practice
- Identify the thread size on your barrel first (1/2×28 or 5/8×24 in most cases).
- Decide which cell size / outer diameter fits your preferred balance of size, weight, and capacity.
- Confirm the bore size is appropriate for the calibers you will use.
- Double-check actual measurements when possible, especially when mixing components from different manufacturers.
Recommended Components by Size
Here are popular options that follow the common size standards outlined above:
- 10″ Aluminum Modular Kit (1.58″ OD / B-Cell style) — Dual 1/2×28 & 5/8×24 thread protectors
- 10″ Stainless Steel Modular Kit — Durable 304 stainless with dual-thread options
- Adaptive Dry Storage Cups (1.375-24) — Compatible with many B-Cell modular tubes
- 1.375×24 Piston Booster — For systems that use the common booster interface
Browse All Compatible Kits & Parts →
FAQs
What does “Cell Size” actually mean?
Cell size is a naming convention used to describe the outer diameter of the tube. B Cell is commonly 1.375″, C Cell is smaller, and D Cell is larger (around 1.500″). The letter is just a convenient label — the measured OD is what matters most.
Is 1/2×28 or 5/8×24 more common?
1/2×28 is extremely common on AR-15s, many 9mm firearms, and rimfire rifles. 5/8×24 is the standard for most .308 / AR-10 style platforms and many larger rifle calibers.
Can I use a larger bore size with a smaller caliber?
In most cases yes. A .30 caliber bore can generally handle 5.56 or 9mm safely. However, a small bore must never be used with a larger caliber.
What is the 1.375×24 thread used for?
1.375×24 is a common rear mounting thread found on many modular tubes and booster-style interfaces. It is not the thread on the firearm’s muzzle.
Do all manufacturers use the same cell size names?
No. While B, C, and D Cell are widely recognized, some brands use their own naming or slightly different measurements. Always verify the actual outer diameter when possible.
How do I know which size I need?
Start with your barrel’s thread pitch, then choose the outer diameter (cell size) that matches the capacity and handling characteristics you prefer. Finally, confirm the bore size is safe for your ammunition.
Final Tips
- When in doubt, measure your barrel threads with a thread gauge or consult the manufacturer’s specifications.
- Keep a simple record of the thread size of each firearm you own — it saves time later.
- Modular systems that share the same rear thread (such as 1.375×24) make it easier to mix and match components.
This size guide is intended to help you quickly understand the key dimensions used across tubes, thread protectors, and related components. With a clear grasp of cell size, thread pitch, and bore diameter, selecting the right parts becomes much more straightforward.