Plastic Hex Bar: Sizes, Materials & Machining Uses

Plastic hex bar is hexagonal-cross-section engineering plastic supplied in sizes from 1/4" to 4" across flats, most commonly in Nylon 6/6 and Acetal (Delrin). The hexagonal profile lets you hold the bar in a standard socket or hex collet for turning and secondary operations, and provides flat surfaces for wrench-driven torque when used directly as a functional part. Hex bar is the practical form for machined knobs, standoffs, adjusting nuts, plug gages, and mechanical stops — anywhere a hex head is integral to the design.

TL;DR

• Primary materials: Nylon 6/6 and Acetal (Delrin); PEEK and PVDF available on special order
• Size range: 1/4" to 4" across flats (AF), in standard hex increments
• Extruded in 4-foot lengths; custom cut-to-length available
• "Across flats" (AF) is the nominal dimension; actual AF tolerance is ±0.010"–±0.020" depending on size
• Ideal for: hex-head knobs, jam nuts, adjusting screws, threaded standoffs, mechanical stops
• Holds in a lathe with a hex collet chuck for rapid, repeatable part turning
• Key advantage over round rod: eliminates one fixturing step when a wrench flat is required on the finished part

Hex Bar Size Table by Material

PEEK hex bar and PVDF hex bar are produced to order from extruded round rod milled to hex profile. Lead time is typically 3–7 business days for special hex sizes.

Materials Available in Hex Bar

Nylon Hex Bar

Nylon 6/6 hex bar is the most widely used plastic hex form. Its combination of toughness (Izod impact: 1.0–2.0 ft-lb/in notched), moderate strength (10,000–12,000 psi tensile), and machinability makes it suitable for a broad range of fastener and mechanical-stop applications. Natural (off-white) Nylon hex bar is FDA-compliant for incidental food contact. MoS₂-filled Nylon hex bar adds dry-film lubrication and is preferred where the finished part will thread into metal with repeated installation cycles — the MoS₂ prevents galling on thread flanks.

Moisture absorption is the primary dimensional concern with Nylon hex bar. The AF dimension can grow 0.004"–0.008" per inch of size from dry to equilibrium moisture conditions. For wrench-fit applications requiring tight clearance, machine Nylon hex bar at or near its equilibrium moisture content and verify the fit after equilibration.

Acetal Hex Bar

Acetal (Delrin) hex bar is the premium choice for precision hex components. Its near-zero moisture absorption (0.25% at saturation) means the across-flats dimension is stable from machining through installation and service — a significant advantage over Nylon for precision wrench fits and gaged applications. Acetal threads machine cleanly and resist the burring that plagues softer thermoplastics. Natural Acetal is FDA-compliant; black Acetal contains carbon black colorant and is not food-grade.

Acetal hex bar produces finished parts that hold tighter tolerances over time than Nylon. It is the first choice for precision adjusting knobs, micrometer-style lock nuts, gage bodies, and any component where dimensional drift is unacceptable. Tensile strength: 9,500–10,000 psi; hardness: Rockwell M90; compressive strength: 18,000 psi.

PEEK and PVDF Hex Bar

For applications requiring elevated temperature resistance, PEEK hex bar provides continuous service to 480°F (250°C) and resists all common industrial solvents. It is machined from precision-ground hex blanks or extruded hex bar on order. PVDF (Kynar) hex bar provides chemical inertness for semiconductor and pharmaceutical hex fittings and manually adjustable compression fittings.

How Plastic Hex Bar Is Made

Extrusion Through Hex Die

Nylon and Acetal hex bar is produced by screw extrusion through a hex-profile die. Molten polymer is forced through the die, and the hexagonal cross-section is formed by six flat die surfaces. The extrudate is pulled through a vacuum calibrator that maintains the across-flats dimension. Because the corners of a hex profile cool faster than the flat faces, there is typically a small amount of corner rounding (R ≈ 0.010"–0.030" depending on AF size) — this is normal and expected. If sharp corners are required, the hex can be machined from square or round bar.

Flat-Milling from Round Bar

When hex bar is not stocked in a specific material or size, it is machined from round rod. A piece of round bar is held in a precision V-block or rotary fixture and milled to the hex profile across all six flats in a single setup. This method produces sharper corners and tighter AF tolerance (±0.003"–±0.005") than extruded hex. Cost is higher, and minimum lot sizes apply.

Specifications & Tolerances

Across-Flats Tolerance

Corner Radius

Extruded hex bar has a natural corner radius of approximately 0.010"–0.030". If a finished part must fit into a hex socket with minimum clearance, verify the socket's internal corner relief against the hex bar corner radius.

Length

Standard lengths are 4 ft (48"). Cut-to-length sections are available with a saw-cut tolerance of ±0.125" (standard) or ±0.030" (precision CNC cutoff).

Use Cases: Knobs, Stops, and Fasteners

Hex-Head Knobs

The most common use for plastic hex bar is producing hex-head knobs — hand-tightened fasteners for jig plates, machine guards, and equipment covers. Turning the cylindrical shank and threading it takes one lathe setup when the bar is held in a hex collet. The hex head is pre-formed, so no secondary milling of wrench flats is needed. Acetal is preferred for knobs requiring tight engagement torque; Nylon for knobs subject to vibration that could back off a rigid thread.

Mechanical Stops and Adjusters

Hex bar sections threaded onto a rod or shaft serve as lock-adjustable stops. The wrench flats allow precise positioning with a standard open-end wrench. Acetal and Nylon stops are common on conveyor guides, limit-switch actuators, and jig positioners — they resist corrosion, reduce noise vs. metal stops, and absorb impact without galling the mating shaft.

Threaded Standoffs and Spacers

Plastic hex standoffs are drilled and tapped through, creating a through-threaded hex body for PCB mounting, panel spacing, and structural assembly. Standard hex AF sizes correspond to common wrench sizes (1/4"–1" AF for #4–40 through 3/8"-16 threads). Nylon standoffs are used in low-load electronics applications; Acetal for higher-precision structural spacers.

Cutting & Finishing

Sawing to Length

Hex bar should be cut on a horizontal band saw or miter saw with a fine-tooth blade. The six-sided profile can rock in a standard vise — use V-blocks or a hex vise jaw to clamp the bar flat-to-flat for stable cuts. Blade TPI: 14–18 for Nylon and Acetal hex under 1" AF; 10–14 for larger sizes.

Turning in a Hex Collet

A hex-bore collet chuck holds plastic hex bar for CNC lathe turning of shanks, threads, and faces. The hex collet provides positive drive without slipping and is faster to set up than a 3-jaw chuck for production runs.

Threading

Nylon and Acetal hex bar threads on a CNC lathe or with standard taps and dies. Use sharp, polished-flute taps; do not use spiral-point (gun) taps in blind holes — plastic chips pack into the flute and can split the material. For production threading, thread mills or single-point threading on CNC delivers best results and avoids the binding that can split thin-wall sections.

More related guides

Common materials and applications stocked in this form:

Top materials

• PEEK
• UHMW
• Delrin
• G10 and FR4

Applications

• Bushings & bearings
• Wear strips & guide rails
• Electrical insulation

Industries

• Aerospace plastics
• Food & beverage plastics
• General industrial