Last Updated 23 minutes ago
Filmmaking Dictionary: Number 3 / 3/8″-16 UNC Thread
Definition
A 3/8″-16 UNC thread is a common mounting thread used on camera-support and grip equipment. The first number gives the nominal major diameter, three-eighths of an inch. The second means 16 threads per inch.
The nominal diameter is 9.525 mm and the thread pitch is approximately 1.588 mm. Those conversions do not make it a metric thread. A similar-looking metric screw is not an interchangeable substitute.
Where It Appears
The thread is often found on tripod heads, mounting plates, support accessories and adapters. It is larger than the familiar 1/4″-20 camera screw, but the thread size alone does not establish how much weight an attachment can safely support.
The complete connection includes the screw material, engagement length, receiving part, contact surface and load direction. A strong screw in a weak accessory or a shallow socket remains a weak connection.
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Thread Length and Engagement
A screw that is too long can bottom out before the equipment is clamped against its mounting surface. The handle may feel tight even while the item remains loose. It may also damage internal parts where the receiving hole is not intended for that length.
A screw that is too short may engage too little of the female thread. Use the screw and engagement specified for the equipment rather than choosing whatever protrudes through the plate.
Practical Example
A camera plate with a captive 3/8″-16 screw is fitted to a compatible support. Before loading the assembly, the operator checks that the screw enters smoothly, the mating surfaces sit flat and the plate cannot rotate or lift. Any locating pins or anti-twist features must also align correctly.
Connection Checks
- Confirm both diameter and thread pitch.
- Start the screw gently by hand to detect misalignment.
- Check usable depth and the required engagement.
- Use approved anti-rotation features where the system provides them.
- Inspect damaged, dirty or cross-threaded parts before use.
- Follow the equipment manufacturer’s mounting and load instructions.
Common Mistakes
An adapter from 3/8″-16 to 1/4″-20 changes compatibility; it does not automatically preserve the original assembly’s load rating. Stacking adapters can also increase leverage or introduce additional points that loosen.
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Frequently Asked Questions
Does ‘3/8’ identify the screw length?
No. It identifies nominal thread diameter. Length is specified separately.
Is every 3/8-inch thread compatible?
No. The pitch and thread form must also match.
Related Terms
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