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The 5.5mm pin is one of the rarer AK trunnion setups, and if you own a rifle built around it you already know the stock options are slim. This Midwest Industries adapter fixes that by replacing the standard rear trunnion with a Mil-Spec 1913 Picatinny rail, opening the door to a huge range of modern 1913-style fixed and side-folding stocks and braces. It's a favorite for KP-9 and KP-104 builds along with certain Romanian, Polish, and Bulgarian folders that use the original 5.5mm pin.
The body is machined from 6061 aluminum with a hardcoat anodized finish, so it stays light without giving up toughness. The real trick is the pair of steel tension blocks. Once you snug down the tension screws, the adapter clamps into the receiver with no wobble, which is what you want when you're putting a stock through the recoil of 7.62×39 or any other AK chambering. Feedback from folks running these consistently points to a rock-solid, wobble-free lockup that holds zero and doesn't shift after hundreds of rounds.
With the right tools this is roughly a 15-minute job. You slide the adapter in just short of the tension blocks, seat the blocks, then work the unit the rest of the way into the receiver until it contacts the rear. A few taps with a rubber mallet is common on AK builds. Depending on your specific rifle you may need to trim or clear the stock tang, and a dab of thread locker on the tension screws before heading to the range is smart insurance.
One thing worth knowing up front: this is the 5.5mm pin version only. It won't fit standard fixed-stock AKs, Yugo pattern rifles, or guns using different trunnion specs, so confirm your rifle runs a 5.5mm folding stock trunnion before ordering. Made in the USA and backed by a lifetime warranty from Midwest Industries.
This version is built specifically for AK factory folders that use the 5.5mm rear trunnion pin, such as the KP-9 and KP-104 along with several Romanian, Polish, and Bulgarian folders. It will not fit standard fixed-stock AKs, Yugo pattern rifles, or guns with different trunnion specs. Check that your rifle runs a 5.5mm folding stock trunnion before ordering.
It replaces the trunnion with a Mil-Spec 1913 Picatinny rail, so you can mount any 1913-style fixed or side-folding stock or brace. That means adjustable carbine stocks, minimalist stocks, fixed rifle stocks, and pistol braces all become fair game. It's a big jump in options compared to traditional AK stock choices.
It uses a pair of steel tension blocks that clamp into the receiver when you tighten the tension screws. Once dialed in, the fit is snug and wobble-free, and users report it holding solid through hundreds of rounds without loosening. A little thread locker on the screws is a good habit before shooting.
For most rifles it goes in around 15 minutes with the right tools, but additional fitting can vary by firearm. Some builds may need the stock tang trimmed or a little material cleared for a clean fit, and a rubber mallet often helps seat it fully. If you plan to run a side-folding accessory, confirm it clears before committing.
| UPC | 812102034315 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | MI-AK-PEPA-5.5 |
| Color | Black |
| Length | 5.7500 |
| Model | |
| Product Type | Adaptor |
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