An 11/16″ wrench does not fit any standard US bolt size perfectly, but it is the closest SAE match for an M10 metric bolt with a 17 mm head.
If you’re holding an 11/16″ wrench and wondering what bolt it actually fits, you’ve run into a gap in the standard US hex bolt system. No common SAE bolt diameter uses exactly 11/16″ as its wrench size. The real-world answer comes from the metric side: an M10 bolt’s 17 mm hex head is only 0.46 mm smaller than 11/16″ (17.46 mm), making it the practical match when metric tools aren’t available — though the fit comes with important limits.
No Standard US Bolt Uses an 11/16″ Wrench
Standard US bolt head sizes follow a fixed pattern: each nominal bolt diameter has a specified across-flats wrench size. In the common UNC/UNF thread series, the 11/16″ socket size simply does not match any standard bolt diameter. A 3/8″ diameter bolt takes a 9/16″ wrench, a 7/16″ bolt uses 5/8″, and a 1/2″ bolt jumps to 3/4″. The 11/16″ slot exists between widely used sizes, used mainly for specialty fasteners or older equipment. If you’re working on a modern US-standard bolt, you likely need a different wrench.
The M10 Metric Match: Close But Not Perfect
An M10 metric bolt has a hex head measuring exactly 17 mm across the flats. Since 11/16″ equals 17.46 mm, the difference is just under half a millimeter — about the thickness of a credit card. For light-duty or non-critical work where part of a turn is enough, this match works reliably. Many mechanics keep an 11/16″ wrench as their “SAE M10” tool for brackets, covers, and low-torque fasteners. For high-torque applications, safety-critical assemblies, or where the bolt’s grip matters, the 0.46 mm gap can cause rounding — use the correct 17 mm metric wrench instead.
Quick Reference: Which Bolt Takes Which Wrench
| Bolt Diameter | Standard Wrench Size | Notes |
|---|---|---|
| 3/8″ (US standard) | 9/16″ | Common automotive and hardware size |
| 7/16″ (US standard) | 5/8″ | Frequent on brackets and smaller assemblies |
| 1/2″ (US standard) | 3/4″ | Heavy-duty structural and suspension work |
| M10 (metric) | 17 mm | 11/16″ is the closest SAE substitute |
| 11/16″ itself | (no standard match) | Fits M10 with slight play; used in non-precision settings |
When the 11/16″ Wrench Works
Three scenarios make this wrench useful: (1) you have only SAE tools and need to turn an M10 bolt on a low-stress part like a valve cover or light bracket, (2) you’re working on older farm or industrial equipment where non-standard fasteners appear, or (3) you need to verify a bolt’s size — an 11/16″ wrench that slides over the hex confirms the head measures roughly 17 mm, indicating an M10 bolt. For every other situation, buy or borrow the correct tool.
References & Sources
- Bolt Depot. “US Bolt Head Size Chart.” Confirms no standard US bolt head matches 11/16″.