Optical Thread Size Chart: Metric, Imperial, SM1 and SM2 Threads
Optical lens tubes, filter mounts, camera adapters and optomechanical components often use fine-pitch threads. The following reference table covers common sizes used in semiconductor inspection, AOI and machine-vision equipment.
| Series | Thread | Nominal Diameter | Pitch | Typical Application |
|---|---|---|---|---|
| SM05 | 0.535"-40 | 0.535 in (approx. 13.59 mm) | 40 TPI (0.635 mm) | Approx. Ø1/2" optics, lens tubes and adapters |
| SM1 | 1.035"-40 | 1.035 in (approx. 26.29 mm) | 40 TPI (0.635 mm) | Approx. Ø1" optics, lens tubes and filter mounts |
| SM1.5 | 1.535"-40 | 1.535 in (approx. 38.99 mm) | 40 TPI (0.635 mm) | Approx. Ø1.5" optics and lens tubes |
| SM2 | 2.035"-40 | 2.035 in (approx. 51.69 mm) | 40 TPI (0.635 mm) | Approx. Ø2" optics and large-aperture tubes |
| SM3 | 3.035"-40 | 3.035 in (approx. 77.09 mm) | 40 TPI (0.635 mm) | Approx. Ø3" / 75 mm-class optics |
| C-Mount | 1"-32 UN | 1.000 in (25.40 mm) | 32 TPI (0.7938 mm) | Industrial cameras and machine-vision lenses |
| RMS | 0.800"-36 | 0.800 in (20.32 mm) | 36 TPI (0.7056 mm) | Microscope objectives and adapters |
| M25.5 × 0.5 | Metric fine | 25.5 mm | 0.5 mm | Compact lenses, filters and adapters |
| M32 × 0.5 | Metric fine | 32 mm | 0.5 mm | Optical tubes, mounts and adapters |
| M42 × 1 | Metric | 42 mm | 1.0 mm | Camera lenses and optical adapters |
This chart is for preliminary selection. Thread class, male/female tolerances, engagement length and chamfers can vary; confirm the component drawing or manufacturer specification before machining.
Why Optomechanics Uses Fine Threads
Metric threads are normally written as diameter × pitch, such as M25.5 × 0.5. Imperial threads are commonly identified by diameter and threads per inch (TPI), such as the SM1 specification 1.035"-40. Fine threads provide smaller axial movement per turn and are well suited to thin-wall lens tubes, retaining rings and precisely positioned optical assemblies.
Common SM sizes include SM05, SM1, SM1.5, SM2 and SM3, generally using 40 TPI. SM1 is commonly associated with approximately 1-inch optics, while SM2 is commonly associated with approximately 2-inch optics. The series name is not the actual thread diameter, so machining dimensions must be taken from the full specification.
Semiconductor Inspection and AOI Applications
Semiconductor inspection, automated optical inspection (AOI) and machine-vision systems may use SM-series, C-Mount, RMS or metric fine threads wherever cameras, lenses, lighting, filters and optical modules are mounted or adapted. These parts may also require controlled concentricity, perpendicularity, flange distance and internal light suppression.
Janway Enterprise Co., Ltd. can machine optical tubes, lens mounts, thread adapters, retaining rings and inspection fixtures to customer drawings, including metric and imperial fine threads. When only a mating component or sample is available, we can first review dimensions and manufacturability; production is based on an approved engineering drawing.