In the world of photography, videography, and astrophotography, thread sizes and mount types are more than just technical specs — they’re the foundation for building secure, compatible, and high-performing setups.
Whether you're attaching a lens filter, mounting a camera to a tripod, or connecting your DSLR to a telescope, knowing the right thread sizes, TPI (Threads Per Inch), and mounting standards helps you avoid frustrating compatibility issues and ensures a seamless workflow.
This comprehensive guide explores everything from TPI tripod threads to bayonet lens mounts, filter threads from 20mm to 110mm, C & CS mounts, and standard telescope accessories.
🔩 Section 1: Thread Per Inch (TPI) – Used in Mounts & Tripods
TPI (Threads Per Inch) is typically used in tripod screws, mounting arms, audio gear, and rigging equipment. These are mostly Imperial measurements.
| Thread Size | TPI | Use Case | Found On |
|---|---|---|---|
| 1/4"-20 UNC | 20 | Standard tripod screw | Camera bottoms, QR plates |
| 3/8"-16 UNC | 16 | Pro tripod heads | Fluid heads, boom arms |
| 5/8"-27 UNEF | 27 | Microphone mounts | Audio stands |
| 1/2"-13 UNC | 13 | Heavy rigs | Cinema equipment, studio gear |
Adapters are widely available to convert between these thread sizes.
📏 Section 2: Metric-Based Filter Threads (20mm to 110mm)
Lens filters, adapter rings, and some specialty lenses use metric threads, measured in diameter (mm) and pitch (usually 0.75mm).
🔍 Small Filter Thread Sizes (20mm – 37mm)
| Size | Common Uses |
|---|---|
| 20mm | Compact lenses, webcams |
| 22mm | Compact or action cameras |
| 25.5mm | CS-mount lenses |
| 27mm | Small format fixed lenses |
| 30mm / 30.5mm | Camcorders, compact zooms |
| 32mm / 34mm / 35mm | Specialty lenses, microscopes |
| 37mm | Point-and-shoot cameras, compact mirrorless |
➡️ Often used in compact devices, microscopes, and older or specialized equipment.
🔍 Standard to Large Filter Threads (39mm – 110mm)
| Size | Use Case |
|---|---|
| 39mm | Leica M lenses |
| 40.5mm | Compact mirrorless, camcorders |
| 43mm / 46mm | Olympus, Fuji lenses |
| 49mm / 52mm | Entry-level DSLRs |
| 55mm / 58mm / 62mm | Kit lenses, mid-range primes |
| 67mm / 72mm / 77mm | Pro zooms & primes |
| 82mm | Ultra-wide & fast lenses |
| 86mm | Canon RF 28–70mm f/2 |
| 95mm | Canon RF 85mm f/1.2L |
| 110mm | Super-telephoto & cinema lenses |
Pro tip: Filter sizes are typically printed on the front rim of your lens with a ⌀ symbol (e.g., ⌀77mm).
🔄 Section 3: Bayonet Mounts – Quick-Attach Lens Mounting Systems
Bayonet mounts are mechanical twist-lock systems for securely attaching lenses to camera bodies. Each system is brand-specific.
| Mount | Brand | Use |
|---|---|---|
| Canon EF / EF-S | Canon DSLRs | |
| Canon RF | Canon mirrorless (R-series) | |
| Nikon F | Nikon DSLRs | |
| Nikon Z | Nikon mirrorless | |
| Sony E / FE | Sony mirrorless APS-C / Full Frame | |
| Fujifilm X | Fuji mirrorless APS-C | |
| Micro Four Thirds (MFT) | Olympus / Panasonic | |
| Leica M / L | Leica rangefinder / alliance |
➡️ Lens mount adapters are available to bridge different systems, e.g., Canon EF to Sony E.
🔭 Section 4: Telescope Mounts – Optical Threading Standards
Astrophotographers often integrate DSLRs or dedicated astronomy cameras with telescopes. Here are the most common threads and mounts:
🌌 Standard Eyepiece Mounts
| Size | Use |
|---|---|
| 1.25" (31.75mm) | Most common for amateurs |
| 2" (50.8mm) | Wider views, better for deep sky |
➡️ These accept visual back adapters, diagonals, and camera adapters.
🔬 C & CS-Mount Threads
| Mount | Thread | Use |
|---|---|---|
| C-Mount | 1" x 32 TPI or M25.4x0.75 | Industrial, astro cameras |
| CS-Mount | M25.4 x 0.5 | Compact CCD/CMOS cameras |
C-Mount vs CS-Mount: CS has a shorter flange focal distance (12.5mm vs 17.5mm). Adapters allow interchangeability with spacing rings.
🔧 Other Astro Threads
| Thread | Use |
|---|---|
| T2 (M42 x 0.75) | Universal for DSLR-to-telescope |
| M42 x 1.0 | NOT the same as T2 – vintage lenses |
| M48 x 0.75 | Larger astro filters, full-frame setups |
| M54 x 0.75 | Premium focusers |
| SCT Threads (2”/24 TPI) | Schmidt-Cassegrain telescopes |
➡️ Use T-rings and adapters to attach cameras securely and maintain focus distance.
🛠️ Section 5: Must-Have Adapters & Converters
Adapting is essential in any hybrid setup. Here's what you should keep handy:
| Adapter Type | Purpose |
|---|---|
| 1/4"-20 to 3/8"-16 | Tripod screw conversion |
| Step-Up/Step-Down Rings | Use filters on mismatched lenses |
| C to 1.25" Adapter | Attach astro cameras to telescope eyepieces |
| T-Ring + T-Adapter | Mount DSLR to telescope |
| Lens Mount Adapters | Use lenses across brands |
| Hot Shoe Adapters | Mount lights, monitors, mics |
| Speed Boosters | Lens adapter with optics to regain field of view |
💡 Final Tips
- ✅ Always verify thread pitch and size (especially with M42/M48/M54!)
- ✅ Use metal adapters for strength and durability.
- ✅ Never force threads — mismatching can damage both pieces.
- ✅ Label your adapters to save time during shoots or setups.
🏁 Conclusion
From 1/4"-20 tripod threads to 110mm lens filters, from bayonet lens mounts to telescope C and T2 adapters, the variety of threading in photography and astrophotography can seem overwhelming. But with this guide, you’ll be equipped to identify, adapt, and build out your setup with confidence.
Whether you're a hobbyist mounting a filter on a vintage lens or an astrophotographer connecting a DSLR to a deep-space telescope, this reference will help you get the connection right every time.
📸🔭 The Ultimate Guide to Photography and Telescope Thread Sizes, TPI, and Mounts