--- title: "5/8\"-27 UNS tap drill 15 mm, clearance 16.67 mm" description: "5/8\"-27 UNS: tap drill 15 mm, clearance hole 16.67 mm, 23.81 mm hex. Full thread dimensions, how to identify it, and torque." url: https://atoneplace.net/fastener/five-eighths-27/ site: "At One Place" --- # 5/8"-27 UNS thread **5/8"-27 UNS tap drill: 15 mm** Clearance hole 16.67 mm · 23.81 mm hex 5/8"-27 UNS is a extra-fine Unified inch thread with a 15.875 mm (0.625") major diameter and 27 threads per inch (0.941 mm pitch). Tap it with a 15 mm drill; drill 16.67 mm to pass a bolt through. ## The numbers - **Designation:** 5/8"-27 UNS - **Major diameter:** 15.875 mm / 0.625" - **Minor diameter:** 14.857 mm - **Pitch:** 27 threads per inch (0.941 mm pitch) - **Tap drill (75% thread):** 15 mm — 15 mm - **Clearance hole (close fit):** 16.67 mm / 0.656" - **Hex across flats:** 23.81 mm ## How to measure what you have 1. Measure across the thread crests with calipers. A used 5/8"-27 UNS reads a little under 15.875 mm — the crests are truncated by the standard, then worn and plated, so anything from about 15.5 mm up is consistent with this size. 2. Count the threads crossing one inch. This one gives 27. 3. A thread pitch gauge settles it in seconds and costs very little. Guessing between a coarse and a fine thread of the same diameter is the usual way a thread gets stripped. ## Tightening torque No torque figure is given for this size. Small and fine threads like this are generally not supplied to a strength grade, and in most assemblies the tapped material strips before the fastener yields — so a published bolt torque would be the wrong limit to work to. Tighten to snug plus a small turn, or use the figure the manufacturer of the part specifies. ## Where this size turns up - Microphone stand and boom arm threads - Microphone clips, shock mounts and adaptors - Studio and stage stand accessories > A unified special that exists almost entirely for audio: microphone stands, clips and boom arms. Outside the US, stands are often 3/8"-16 with a 5/8"-27 adaptor in the box. The tap drill is the awkward part, because 27 threads per inch does not line up with the fractional drill series: 75% engagement wants 0.589 in and no fraction hits it. A 15 mm bit (0.591 in) is the nearest stocked drill and leaves about 73%. Tap sellers often ship 37/64 in (0.578 in), which is close to a full thread and much harder to cut, and some charts list 19/32 in (0.594 in), which leaves only about 65%. ## Other threads at this diameter *Same diameter, different pitch. Forcing the wrong one strips the thread in a turn or two.* | Thread | Pitch | Tap drill | Clearance | | --- | --- | --- | --- | | 5/8"-11 UNC | 11 tpi | 17/32" | 16.67 mm | | 5/8"-18 UNF | 18 tpi | 37/64" | 16.67 mm | ## Common questions ### What size drill for an 5/8"-27 UNS tap? 15 mm (15 mm), which gives about 75% thread engagement. ### What clearance hole for 5/8"-27 UNS? 16.67 mm for a close fit — enough to pass the bolt without slop. ### What spanner fits 5/8"-27 UNS? 23.81 mm across the flats on a standard hex head. ## Related pages - [5/8"-11 UNC](https://atoneplace.net/fastener/five-eighths-11/) - [5/8"-18 UNF](https://atoneplace.net/fastener/five-eighths-18/) - [9/16"-12 UNC](https://atoneplace.net/fastener/nine-sixteenths-12/) - [9/16"-18 UNF](https://atoneplace.net/fastener/nine-sixteenths-18/) - [1/2"-13 UNC](https://atoneplace.net/fastener/half-13/) - [3/4"-10 UNC](https://atoneplace.net/fastener/three-quarters-10/) - [1/2"-20 UNF](https://atoneplace.net/fastener/half-20/) - [3/4"-16 UNF](https://atoneplace.net/fastener/three-quarters-16/) - [1/2"-28 UNEF](https://atoneplace.net/fastener/half-28/) - [3/4"-20 UNEF](https://atoneplace.net/fastener/three-quarters-20/) - [7/16"-14 UNC](https://atoneplace.net/fastener/seven-sixteenths-14/) - [7/16"-20 UNF](https://atoneplace.net/fastener/seven-sixteenths-20/) ## Sources - Official vendor product documentation — At One Place (/about/)