What Is a Hex Bar?
A hexagonal bar (commonly called hex bar) has a cross-section in the shape of a regular hexagon — six equal flat faces at equal angles. It is the standard raw material for machining valve bodies, bolt heads, fittings, nuts, and any component that needs a hexagonal gripping surface or is machined from a hex blank on a CNC lathe.
The Two Ways to Measure a Hexagon
A hexagon has two key external dimensions:
- Across Flats (AF): The distance between two opposite flat faces. This is measured with a pair of parallel calipers placed flat against two opposite faces.
- Across Corners (AC): The distance between two opposite corners (the longest dimension across the hexagon).
For any given hexagon, AC is always larger than AF. The relationship is:
AC = AF × 1.1547
For a 27mm AF hex bar, the across-corners dimension is: 27 × 1.1547 = 31.18mm
Why AF Is the Standard for Specifying Hex Bar
Spanners and sockets fit across flats. A 27mm spanner grips a hexagonal component at its flat faces — 27mm apart. When a machinist turns a hex bar down to make a valve body or bolt head, the critical finished dimension is the AF measurement — because that is what the wrench or socket must fit.
Specifying hex bar by AF means the raw material and the finished component share the same reference dimension. A 27mm AF hex bar produces components that fit 27mm spanners.
If hex bar were specified by AC instead, a 27mm AC bar would produce components with a 23.4mm AF — fitting a 23mm spanner. This mismatch between raw material spec and finished component spec would cause constant confusion on the shop floor.
Industry standard: In India, Europe, and most of the world, hex bar is specified and purchased by Across Flats. Always.
Common AF Sizes and Their Applications
| AF Size | Common Applications |
|---|---|
| 13–19mm | Small fasteners, fittings, instrument valves |
| 22–27mm | Medium valve bodies, industrial fittings |
| 32–41mm | Large valve stems, gate valve components |
| 46–53mm | Heavy-duty valve bodies, flange fittings |
What "19mm AF" Means on Your Drawing or Purchase Order
When a drawing specifies a hex component with a 19mm AF dimension, the correct raw material is 19mm AF hex bar. The machinist will either:
- Leave the hex faces unmachined (if the bar diameter tolerance is acceptable)
- Turn the ends on a lathe and leave the hex midsection at the bar's AF dimension
Either way, the bar's AF = finished component's AF.
How Navkardeep Supplies Hex Bar
Our hex bars are manufactured and supplied to Across Flats (AF) dimensions as standard:
| Specification | Details |
|---|---|
| Size range | 8mm AF to 53mm AF |
| Surface finish | Hot Rolled, Hot Rolled Annealed Pickled, Drawn (Bright) |
| Lengths | 3000mm to 6000mm |
| Grades | SS202, SS304, SS316, SS316L, SS430, SS410 |
| Standard | IS 6911, ASTM A276 |
Supply with MTC showing SPECTRO-verified chemistry.
Our weight calculator calculates hex bar weight by AF dimension — the correct standard — and includes a note explaining that AF = Across Flats, the flat-to-flat measurement.