Hex Jam Nuts
What are Hex Jam Nuts and how do they work?
Hex jam nuts—also called jam nuts or thin hex nuts—are low-profile hexagonal nuts used to lock or secure fastener assemblies in tight spaces. Typically about two-thirds the thickness of a standard hex finish nut, a jam nut is tightened against another nut or component to resist loosening from vibration.
Hex Jam Nuts vs Hex Finish Nuts, what’s the difference?
- Thickness: Jam nuts are thinner for low-profile or locking applications; finish nuts are thicker for general fastening.
- Function: Jam nuts often pair with another nut to “jam” the threads; finish nuts are commonly used alone to clamp parts together.
- Use case: Choose jam nuts for limited clearance or to add a lock to an assembly; choose finish nuts for standard clamping strength.
Hex Jam Nut Sizes, Threads & Materials
- Imperial sizes: Common sizes include #6-32, #8-32, #10-24, 1/4"-20, 5/16"-18, 3/8"-16, and 1/2"-13.
- Metric sizes: Typical options include M4, M5, M6, M8, M10, and M12.
- Threads: Coarse (UNC/ISO) for general use; fine (UNF) where greater vibration resistance or precise adjustment is needed.
- Materials & finishes: Stainless steel (18-8/304, 316 for marine), zinc-plated steel, black oxide stainless, brass, and silicone bronze. Select materials to match corrosion needs and base fastener material.
- Standards: Options available to ASME B18.2.2, DIN 439B/ISO 4035, and similar specs.
Installation Tips for Hex Jam Nuts
- Thread the first nut onto the bolt or stud and tighten to the desired preload.
- Run the jam nut down to meet the first nut; hold the first nut with a wrench while tightening the jam nut firmly against it.
- Use matched thread pitch and compatible materials to avoid galling; consider anti-seize on stainless-to-stainless joints.
- For extreme vibration, pair the jam nut with a lock washer, thread-locking compound, or a prevailing-torque nut if clearance allows.
Common Applications for Hex Jam Nuts
- Automotive suspension, steering, and linkage adjustments
- Machinery setups and equipment calibration where thin locking is required
- Construction and structural assemblies with limited clearance
- Electrical and plumbing fixtures, signs, and hardware where a low profile is preferred
Hex Jam Nuts FAQs
Answers to the most common questions about selecting, installing, and using hex jam nuts.
A hex jam nut is a thinner, low-profile version of a standard hex nut. It’s commonly tightened against a full-height nut to create a mechanical lock or used anywhere clearance is limited.
Tighten the full-height nut to clamp the joint, hold it in place, then tighten the jam nut against it. The opposing forces on the threads increase friction and help resist loosening from vibration.
For locking, install and tighten the standard (full-height) nut first, then tighten the jam nut against it. For adjustable linkages, run the jam nut on first, set the position, and snug the jam nut last.
Use jam nuts when you need a <em>low profile</em>, the simplicity of the double-nut method, or when temperatures/chemicals may limit polymer insert lock nuts. For single-nut locking, a prevailing-torque lock nut is often faster.
304/18-8 stainless works for general outdoor exposure. For saltwater/splash zones or harsher chemicals, choose 316 stainless or silicone bronze.
Zinc-plated steel is best indoors or in dry conditions. Outdoors, especially with moisture, stainless or silicone bronze provides longer service life.
Jam nuts are thinner and can round off if over-torqued. Use manufacturer torque charts when available, or reduce torque compared to full-height nuts and rely on the double-nut lock for security.
Inch jam nuts commonly follow ASME/IFI dimensional guidance; metric low nuts often follow DIN 439B or ISO 4035. Match thread size and pitch to your bolt or stud.
The double-nut method usually provides sufficient resistance to loosening. In severe vibration, threadlocker or a prevailing-torque nut elsewhere in the stack can add redundancy.
Start the nut by hand, ensure it spins freely for several turns, and only then use tools. If you feel sudden resistance, back off and re-align.
You can, but be mindful of galvanic corrosion and friction differences. In wet or corrosive environments, matching stainless-to-stainless is preferred.
As a rule of thumb, engage threads at least equal to the bolt diameter (or per your spec). Ensure enough exposed thread remains to fully seat both the standard nut and the jam nut.