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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.
Prices checked
SIG Sauer Stock Adapter - 1913 Interface Folding Knuckle is the third most added stock adapter on GunPartPicker so far in November 2026, behind the Law Tactical AR Folding Stock Adapter Gen 3-M, with about 18% of all stock adapter parts added to builds. That's its 2nd straight month at #3. Builds with this stock adapter are mostly chambered in 5.56 NATO (76%, then .223 Wylde 8%), mostly on mid-length gas (61%, then carbine-length 19%), and mostly AR-15 (95%).
Availability is good: it was in stock at one retailer or another nearly every time we checked in October 2026, and today all 8 retailers we track have it in stock. The best price crept up from $111.02 to $114.46 over October 2026. Buying today, the lowest price is $97.90 at BattleHawk Armory, which matches the best price we saw in October.
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Updated · from real builds on GunPartPicker · Prices checked · refreshed daily across 37 retailers
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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 | $2318.69 |
 | 37 | $6552.34 |
 | 22 | $3007.86 |
 | 27 | $1531.96 |
 | 27 | $2139.46 |
 | 23 | $2442.74 |
 | 30 | $3662.19 |
 | 34 | $7057.81 |
 | 27 | $2084.78 |
 | 25 | $2284.71 |
 | 23 | $3336.73 |
1 global rating
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.
