Check the drawing's thread system, nominal size, pitch and tolerance before approving an SMT nut match. In M3×0.5, 0.5 is pitch in millimetres; in #4-40, 40 is threads per inch. Partial hand engagement does not establish interchangeability.
Read the complete designation
PEM's official catalog lists M3×0.5 and .112-40 (#4-40) in separate metric and Unified tables. Those products provide notation examples only; their structures and availability must not be attributed to Hongchuan SMT nuts.
M3×0.5 denotes a 3 mm nominal thread diameter and 0.5 mm pitch. Pitch is the axial distance between corresponding points on adjacent thread forms. #4 is a numbered size, not 4 mm. A 40 TPI thread has a pitch of 25.4/40=0.635 mm.
| Example | Pitch notation | Pitch in mm |
|---|---|---|
| M3×0.5 | 0.5 mm | 0.500 mm |
| #4-40 | 40 threads/in | 0.635 mm |
| Nut OD or width across flats | External geometry | Does not identify the thread |
Unit conversion does not make threads compatible. Bossard's comparison tool separates diameter, pitch and mechanical properties. Retain the controlled thread designation rather than replacing it with an approximate converted dimension.
Do not force a trial fit
Entry chamfers, thread condition and applied force affect a hand trial. Stop if resistance is abnormal and isolate the sample for inspection; forcing engagement can damage the thread. A hand trial does not define full geometric tolerance or verify usable engagement length.
Check package identification, supplier part number and drawing revision, then use the agreed inspection procedure and correctly specified gauges. The SMT nut GO/NO-GO guide addresses gauging separately. A screw of another thread system is not an inspection gauge.
Keep external fit in the review
For SMT nuts and SMD nuts, provide thread details, finish, usable depth and mating screw information alongside OD or width across flats, overall height, soldering face and PCB land drawing. Matching threads do not establish matching pickup or assembly geometry.
Unverified M3, M4 or other sizes are RFQ requirements, not a claim of available Hongchuan stock. This page supplies no substitution part number or installation torque. If a drawing omits pitch, obtain the designer's confirmed standard and complete requirement before ordering.
Questions
Can a caliper reading near 3 mm confirm M3? A diameter reading alone does not establish pitch, tolerance or thread system.
Can a converted TPI value authorize a purchase change? It supports comparison; substitution still needs drawing and assembly review.
References
PEM catalog metric and Unified examples; Bossard metric/inch fastener comparison.
The cover is an AI thread-spacing concept, not a Hongchuan section or fit test. Depicted geometry is not a manufacturing or interchangeability specification.