DIN 25201 — Double-Stack Lock Washers: Design Guide

DIN 25201

Design and application standard for double-stack lock washer systems. Defines wedge-locking principle: relative rotation of two washers creates wedging effect, converting vibration load into frictional locking force. Covers M3-M48, operating temperature -40°C~+200°C, materials 42CrMo4/51CrV4. Locking performance superior to standard spring washers and nylon-insert lock nuts; vibration life ≥10⁶ cycles.

Clause Summaries

Scope

Applies to bolted joint anti-loosening under vibration conditions in railway, construction machinery, wind power equipment. Covers M3-M48 metric threads, used with grade 8.8/10.9/12.9 bolts.

Wedge-Locking Principle

Staggered wedge faces of the two washers create locking: upper washer follows nut rotation, lower washer embeds radial serrations into the clamped surface. Under vibration, bolt/nut rotation is prevented by wedging — only sliding in wedge direction (locking direction) is possible.

Installation & Tightening Torque

DIN 25201 washers have negligible effect on tightening torque (±3%); no torque correction needed. Install with washer face against the clamped part; ensure lower washer radial serrations fully embed. Post-tightening check: 0.1-0.3mm visible gap between upper and lower washers.

Vibration Testing & Locking Performance

Per ISO 16130 transverse vibration test (Junker test), DIN 25201 washers retain ≥85% initial clamp force after 10⁶ cycles, far exceeding DIN 127 spring washers (<30%) and DIN 985 nylon-insert nuts (50-70%).

Dimension Table

de	di	force	group	h0	t	weight_per_1000
7	3.2	850	M3	0.35	1	0.18
9	4.3	1300	M4	0.4	1.2	0.35
10	5.3	2100	M5	0.5	1.5	0.55
12	6.4	3200	M6	0.6	1.8	0.9
16	8.4	5800	M8	0.75	2.2	2
20	10.5	9200	M10	0.9	2.7	3.8
24	13	14000	M12	1.1	3.2	6.3
30	17	24000	M16	1.4	4	11.5
37	21	38000	M20	1.7	5	22
44	25	56000	M24	2	6	37