AR-15 LPK Pivot Pin Detent Spring

Description

OVERVIEW – PRECISION SPRING FOR POSITIVE PIVOT PIN RETENTION AND FUNCTION

The AR-15 LPK Pivot Pin Detent Spring is one of the smallest but most critical springs in your AR-15 Lower Parts Kit. If you are missing this spring, building a lower from scratch, or replacing a spring that launched across the room during installation — a common experience for every AR builder — this mil-spec replacement ensures your pivot pin functions exactly as designed. The pivot pin detent spring sits behind the pivot pin detent inside the front lug channel of your lower receiver and applies constant pressure to the detent, which engages the grooves in the pivot pin. This tension is what holds your pivot pin in place, preventing it from walking out or falling free, while still allowing you to easily push the pivot pin out when you need to separate the upper and lower receivers for cleaning, maintenance, or breakdown.

Without the correct spring tension, your pivot pin will either be too loose and fall out during handling, or too stiff to push with finger pressure. This replacement spring is wound to exact mil-spec dimensions, wire diameter, and coil count to provide the correct pressure for smooth but secure pivot pin operation. Made from high-quality spring steel and finished for corrosion resistance, it maintains its tension over thousands of open/close cycles and will not take a set, compress flat, or lose strength like cheap aftermarket springs. It is compatible with all standard AR-15, M4, M16, and AR-10 lower receivers that use standard pivot pin detents, including forged, billet, and 80% lowers. Whether you are completing a lower build, performing maintenance, or keeping essential spare LPK springs on your workbench, this pivot pin detent spring is a must-have small part that restores proper retention and function to your takedown assembly.

WHY CHOOSE THIS PIVOT PIN DETENT SPRING

Tiny spring, critical retention function.

1. Mil-Spec Dimensions and Correct Tension for Positive Pivot Pin Retention: The function of the pivot pin detent spring is deceptively important. It lives inside a small blind hole drilled into the front lug area of the lower receiver, and it pushes against the pivot pin detent, which in turn rides in the detent grooves machined into the pivot pin itself. This spring’s tension determines how firmly the pivot pin is held in both the closed (rifle assembled) and open (pivot pin partially out for upper separation) positions. Too weak a spring and the pivot pin will drift out under recoil or handling, causing your upper to separate unexpectedly. Too strong and you will need a punch or tool to move the pivot pin, defeating the tool-less takedown design. This spring is manufactured with the correct wire gauge, outer diameter, free length, and number of active coils to deliver the exact mil-spec spring rate. The result is a pivot pin that stays firmly seated when closed, snaps positively into the open position when pushed, and can still be manipulated with thumb pressure without tools. The spring rate is consistent from batch to batch, so you get the same reliable function every time.

2. High-Quality Spring Steel with Corrosion-Resistant Finish for Long Service Life: Unlike cheap replacement springs made from soft wire that compresses flat after a few months, this detent spring is made from properly tempered spring steel that retains its elasticity and memory over long-term use. The steel is heat-treated to the correct hardness to resist taking a permanent set, even when held under compression inside the receiver for years. The surface is treated for corrosion resistance, protecting against moisture, humidity, gun oils, and cleaning solvents that can cause rust and weaken spring tension. This is especially important because this spring sits inside a channel in the lower receiver where moisture can collect. The ends of the spring are finished cleanly to prevent binding or digging into the detent or the receiver channel. Each spring is inspected for consistent coil spacing and straightness, ensuring it slides freely into the receiver hole without kinking or hanging up. This is a true mil-spec replacement part built for duty, defense, and high-round-count rifles, not a soft hardware store substitute.

3. Essential Replacement for Lost LPK Parts and Lower Builds: If you have ever built an AR-15 lower, you know that the pivot pin detent spring and takedown detent spring are the two most commonly lost parts — they are tiny, under tension during installation, and love to launch across the room. This is why experienced builders keep spares of both on hand. This spring is a direct drop-in replacement for any standard AR-15 lower parts kit. Installation is straightforward: drop the pivot pin detent into its channel, then insert this spring behind it, compressing it with the pivot pin itself as you slide the pivot pin into place, or use a 1/16″ punch to hold the detent down while starting the pivot pin. It works with all standard pivot pin detents and pivot pins. Compatible with all standard AR-15, M4, M16, and AR-10 lower receivers that use mil-spec pivot pin assemblies — including forged, billet, and 80% lowers. Whether you lost your spring, are assembling a stripped lower, or are stocking your armorer’s kit with essential spares, this detent spring ensures your pivot pin stays secure and functional.

RESTORE PROPER PIVOT PIN RETENTION

The AR-15 LPK Pivot Pin Detent Spring delivers mil-spec tension and corrosion-resistant durability for reliable pivot pin function.

SPECIFICATIONS

Type: AR-15 LPK Pivot Pin Detent Spring – Takedown Assembly Spring. Material: Spring Steel – Heat Treated and Tempered. Finish: Corrosion-Resistant. Function: Applies Pressure to the pivot pin detent for Pivot Pin Retention. Compatibility: All Standard AR-15 / M4 / M16 / AR-10 lower receivers using a Mil-Spec Pivot Pin Detent. Placement: Front Lug Channel of Lower Receiver Behind Pivot Pin Detent.