MIDWEST FASTENER CORP 3651 Nylon Insert Lock Nut 3/8-16 Steel Grade 2 Zinc

Lock Nut for Vibration Resistance

This MIDWEST FASTENER CORP 3651 lock nut uses a nylon insert to resist loosening under vibration and torque. It is a Grade 2 steel fastener with a zinc finish, sized at 3/8"-16 thread. The component suits maintenance, repair and assembly tasks where a standard nut might back off over time. Buyers who need a locking fastener for general-purpose mechanical joints will find it fit for purpose.

Upgrade from Standard Hex Nuts

A plain hex nut relies on friction alone and can loosen when equipment vibrates or cycles under load. This lock nut adds a nylon collar that grips the bolt threads, maintaining clamp force without additional lock washers or thread-locking compounds. The jump is worth it when the joint sees repeated movement, shock or thermal cycling that would defeat a standard nut. It is not for applications requiring high-strength Grade 5 or Grade 8 fastener ratings, nor for environments where the nylon insert would exceed its temperature limit.

Simple Thread-On Installation

Installation is a straightforward hand or wrench operation: spin the nut onto the 3/8"-16 bolt until the nylon insert engages, then torque to the required value for the joint. The insert creates prevailing torque on the first use, so the nut cannot be spun freely like a plain nut. What usually goes wrong is re-using the fastener; the nylon deforms during initial tightening and loses locking effectiveness on subsequent assemblies. Cross-threading is also a risk if the bolt threads are damaged or the nut is started at an angle.