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Sig Sauer
Overview
The SIG Sauer Stock Adapter - 1913 Interface Folding Knuckle serves as a crucial assembly component that allows for the attachment of folding stocks to your AR-15 platform. This adapter provides a robust connection for stocks designed to interface with a Picatinny rail, enhancing the versatility of your build while maintaining stability. It's commonly found in mid-length gas system builds chambered in 5.56 NATO, making it a practical choice for those looking to streamline their rifle's profile.
SIG Sauer Stock Adapter - 1913 Interface Folding Knuckle was the second most added stock adapter on GunPartPicker in August 2026, behind the SIG Sauer MCX Stock Adapter KIT, with about 26% of all stock adapter parts added to builds. Down from #1 in July. Builds with this stock adapter are mostly chambered in 5.56 NATO (92%), mostly on mid-length gas (67%, then carbine-length 17%), and mostly AR-15 (84%, then AR-10 16%).
Availability is good: it was in stock at one retailer or another nearly every day in August 2026, and today 8 of the 9 retailers we track have it in stock. It dipped to $94.99 at Sportsmans Outdoor Superstore for a stretch in August 2026, well under its usual $108.99 to $109.99, so sales do come around. Buying today, the lowest price is $88.11 at BattleHawk Armory, which matches the best price we saw in August.
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Aggregated and anonymized data showing how builders use this product
Builds in the community that include the SIG Sauer Stock Adapter - 1913 Interface Folding Knuckle
| Build | Parts | Total |
|---|---|---|
 | 22 | $2258.48 |
 | 37 | $6610.06 |
 | 22 | $2980.17 |
 | 27 | $1572.54 |
 | 27 | $2068.26 |
 | 23 | $2340.77 |
 | 30 | $3643.47 |
 | 34 | $7022.87 |
 | 27 | $2011.30 |
 | 25 | $2406.15 |
 | 23 | $3913.10 |
2 global ratings
Top reviews
The SIG folding adapter latches into the open position with zero play, which is what you need for a stock that takes recoil. 1913 interface gives compatibility with most folding stocks. Lockup is positive both folded and extended. Steel construction feels overbuilt in a good way.
SIG Sauer folding stock adapter for 1913 interface has a rubber butt pad on the included stock end that grips shoulders or plate carriers well. Lockup is positive in both folded and deployed states. Steel construction overbuilt for the application.
