POM-H Rod — Diameters, Lengths & Tolerances
POM-H rod is round bar stock produced from acetal homopolymer (polyoxymethylene homopolymer), the higher-strength grade within the acetal family. Compared to copolymer acetal (POM-C), POM-H offers greater mechanical strength, stiffness, and fatigue resistance, making it the preferred starting stock for demanding precision components operating under elevated mechanical loads or in high-cycle environments.
At a glance:
- Diameter range: standard rod sizes available up to approximately 6" OD
- Standard lengths: 2 ft and 4 ft cut lengths
- OD tolerance: close commercial tolerances
- Material: Acetal Homopolymer — Polyoxymethylene Homopolymer (POM-H)
- Color: Natural (white/off-white)
- Water absorption (24 h / 96 h): 0.05 / 0.1 % — excellent dimensional stability
Standard Diameter Table
POM-H rod is stocked in common diameters to support precision turning and milling:
| Diameter | Standard Lengths | Notes |
|---|---|---|
| 1/4" (0.250") | 2 ft, 4 ft | Pins, small precision parts |
| 1/2" (0.500") | 2 ft, 4 ft | Bushings, spacers |
| 3/4" (0.750") | 2 ft, 4 ft | Cams, followers |
| 1" (1.000") | 2 ft, 4 ft | Gears, high-cycle components |
| 1.5" (1.500") | 2 ft, 4 ft | Larger machined parts |
| 2" (2.000") | 2 ft, 4 ft | Valve and pump components |
| 3" (3.000") | 2 ft, 4 ft | Heavy-section machined parts |
| 4" (4.000") | 2 ft | Large-diameter precision stock |
Contact Ready Plastics to confirm current diameter availability and custom sizes.
Mechanical & Thermal Properties
POM-H delivers higher mechanical performance than copolymer grades. Properties from Ready Plastics specification data:
| Property | Value |
|---|---|
| Density | 1.49 g/cm³ |
| Water absorption (24 h / 96 h) | 0.05 / 0.1 % |
| Flammability (UL 94) | HB |
| Glass transition temp. | -60 °C / -76 °F |
| Melting temperature | 179 °C / 350 °F |
| Heat deflection temp. (HDT, Method A) | 141 °C / 285 °F |
| Service temp. (long term) | 110 °C / 230 °F |
| Service temp. (short term) | 150 °C / 300 °F |
| Tensile strength | 53 MPa / 7,600 psi |
| Tensile modulus | 3,000 MPa / 435,000 psi |
| Elongation at break | 8 % |
| Flexural strength | 85 MPa / 12,000 psi |
| Flexural modulus | 3,000 MPa / 435,000 psi |
| Shore D hardness | 81 |
| Surface resistivity | 10¹⁴ Ω |
| Thermal conductivity | 0.46 W/m·K |
Typical Applications
POM-H rod is specified for components where standard acetal's strength is not sufficient:
- High-load bushings and plain bearings — higher strength supports greater radial loads
- Precision gears in automation systems — fatigue resistance extends gear life in high-cycle drives
- Cam followers and eccentric lobes — superior fatigue resistance for continuous motion mechanisms
- Tooling components requiring dimensional accuracy — trusted for precision tooling where dimensional accuracy is critical
- High-performance valve and pump internals — combination of strength and chemical resistance
- Conveyor system wear components — superior wear resistance for extended service life
Machining POM-H Rod
POM-H rod machines similarly to copolymer acetal with standard carbide or HSS tooling. Its higher crystallinity means it produces slightly more rigid chips and holds tight tolerances well. Use conventional turning parameters with moderate feeds and speeds. Allow freshly machined parts to equalize to ambient temperature before final measurement. For threaded features, standard taps and dies work cleanly at thread-forming diameter recommendations.