ISO 12125 covers the dimensional requirements for fine-thread nylon insert hex flange lock nuts. Reproduced below: the complete size table, and the companion and equivalent standards referenced when ordering to this document.
ISO 12125 — Scope
ISO 12125 is "Prevailing torque type hexagon nuts with flange (with non-metallic insert) with metric fine pitch thread".
Material, property class, surface finish and packaging are governed by separate documents — ISO 898-1 and ISO 898-2 for mechanical property classes, ISO 4042 for electroplated finishes.
Tolerance & Product Grades
ISO 12125 does not divide fine-thread nylon insert hex flange lock nuts into product grades. Tolerances are given as limits on the individual dimensions in the table.
Where a general-tolerance class is cited on the drawing instead, it applies to the dimensions not otherwise toleranced.
Dimensions Specified by ISO 12125
| Size | Pitch P (mm) | c_min (mm) | d_a_max (mm) | d_a_min (mm) | d_c_max (mm) | d_w_min (mm) | Width across corners e (mm) | h_max (mm) | h_min (mm) | m_min (mm) | m_w_min (mm) | Width across flats s (mm) | s_min (mm) | r_max (mm) | Reference standard |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| M8x1 | 1 | 1.2 | 8.75 | 8 | 17.9 | 15.8 | 14.38 | 11.1 | 8.74 | 7.64 | 4.6 | 13 | 12.73 | 0.5 | ISO 12125 |
| M10x1 | 1 | 1.5 | 10.8 | 10 | 21.8 | 19.6 | 16.64 | 13.5 | 10.3 | 9.64 | 5.6 | 15 | 14.73 | 0.6 | ISO 12125 |
| (M10x1.25) | 1.25 | 1.5 | 10.8 | 10 | 21.8 | 19.6 | 16.64 | 13.5 | 10.3 | 9.64 | 5.6 | 15 | 14.73 | 0.6 | ISO 12125 |
| M12x1.5 | 1.5 | 1.8 | 13 | 12 | 26 | 23.8 | 20.03 | 16.1 | 12.57 | 11.57 | 6.8 | 18 | 17.73 | 0.7 | ISO 12125 |
| (M12x1.25) | 1.25 | 1.8 | 13 | 12 | 26 | 23.8 | 20.03 | 16.1 | 12.57 | 11.57 | 6.8 | 18 | 17.73 | 0.7 | ISO 12125 |
| (M14x1.5) | 1.5 | 2.1 | 15.1 | 14 | 29.9 | 27.6 | 23.36 | 18.2 | 14.8 | 13.3 | 7.7 | 21 | 20.67 | 0.9 | ISO 12125 |
| M16x1.5 | 1.5 | 2.4 | 17.3 | 16 | 34.5 | 31.9 | 26.75 | 20.3 | 17.2 | 15.3 | 8.9 | 24 | 23.67 | 1 | ISO 12125 |
| M20x1.5 | 1.5 | 3 | 21.6 | 20 | 42.8 | 39.9 | 32.95 | 24.8 | 20.3 | 18.7 | 10.7 | 30 | 29.16 | 1.2 | ISO 12125 |
Companion Standards
ISO 12125 controls only the geometry of fine-thread nylon insert hex flange lock nuts. The mechanical strength is set by ISO 898-1 (bolts, screws and studs) or ISO 898-2 (nuts); the surface finish is governed by separate finish standards such as ISO 4042 for electroplating. For corrosion testing, the relevant document is ISO 9227 (neutral salt spray).
When to Specify ISO 12125
Choose ISO 12125 for international engineering work and OEM supply where ISO standards are the contractual reference. It is the default modern specification for fine-thread nylon insert hex flange lock nuts.
Custom manufacturing · Made to drawing
Need a nut to this standard in a non-standard size?
Parts built to ISO 12125 are already in the catalog, so a special is usually a variation on existing tooling rather than a new design — which is what keeps the cost down. Made by cold heading or tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
