Square Head Machine Bolt
- Square-head through-bolt — the workhorse fastener of pole-line hardware
- ANSI C135.1, hot-dip galvanized to ASTM A-153
- Thread 1/2 / 5/8 / 3/4 in; lengths to 42 in
- Semi-cone point on 8 in and longer bolts
- Square nut supplied; takes square / curved washers
- Mounts crossarms, brackets, clamps and braces to the pole
Technical Specifications
| Catalog | Thread | Length (in) | Point | Nut | Surface |
|---|---|---|---|---|---|
| RAX-MB-12 | 1/2 in | 3–14 | Cone ≥8 in | Square | HDG |
| RAX-MB-58 | 5/8 in | 4–24 | Cone ≥8 in | Square | HDG |
| RAX-MB-34 | 3/4 in | 6–42 | Cone ≥8 in | Square | HDG |
| Custom | Other sizes / configurations — send your conductor & structure spec | ||||
Application & Installation
Where it is used
The square-head machine bolt is the general through-bolt of overhead line construction — it fastens crossarms, brackets, clamps, braces and bands to the wood or steel pole. The square head resists turning against a flat surface and the square nut is removable years later; it is the most-used fastener on any line.
Installation sequence
- Select the thread and length for the members being joined.
- Bore the pole / arm for the bolt shank.
- Pass the bolt through with a square washer under the head.
- Fit the square washer and nut on the far side.
- Tighten so the members are drawn tight without crushing wood.
Buyer’s Guide: Square Head Machine Bolt
1. What a Machine Bolt Does
A square-head machine bolt is a plain through-bolt that clamps two members together — crossarm to pole, bracket to arm, clamp to structure. It carries the bulk of the mechanical fastening on a line, which is why it is stocked in every thread and length.
2. Square Head & Nut
The square head bears against a flat washer or timber and resists turning as the nut is run up; the square nut is easy to grip with a line wrench and to free years later. Both are larger-bearing than a hex for the same thread.
3. Thread & Length to ANSI C135.1
Machine bolts follow ANSI C135.1 in 1/2, 5/8 and 3/4 in threads, in lengths from a few inches to 42 in. Size the length for the stacked member thickness plus washer and nut, leaving a few threads showing.
4. Semi-Cone Point
Per C135.1, bolts 8 in and longer carry a semi-cone point so they start easily through stacked holes and timber. Shorter bolts have a plain chamfered end.
5. Galvanizing
Hot-dip galvanized to ASTM A-153, with the nut tapped oversize to run over the zinc. Built for decades of outdoor service on the pole.
6. Washers & Pairing
Use a square flat washer on steel and a square curved washer on round poles to spread the bearing. Order the matching washers and nuts with the bolts.
