STAINLESS STEEL MEDIUM SPLIT LOCKWASHERS ASME B18.21.1

Medium Split Lockwashers ASME B18.21.1 — ASME B18.21.1 is the US inch-series equivalent of the DIN 127 split spring washer - a single-turn helical coil, cut through at one point, that compresses axially as the fastener is tightened and presents biting edges at the split ends to resist back-rotation, working on exactly the same principle as its metric counterpart but sized to imperial fastener diameters. Medium identifies the regular-duty weight within the standard, which defines different thickness series - light, medium, and heavy - for the same nominal washer diameter, with medium being the standard general-purpose choice unless a specific application calls for the lighter or heavier alternative. It is specified in general mechanical assemblies built to US or imperial fastener standards, wherever a split-ring spring lock washer is wanted to provide some preload retention and resistance to vibration-induced loosening, in the same role DIN 127 fills on metric equipment. As with its metric equivalent, it should not be treated as a high-reliability locking method for safety-critical assemblies: the spring force and edge bite it provides are genuinely useful for everyday fixings, but where failure risk is high, a more positive method - a nylon insert nut, tab lock, or castellated nut with a split pin - is the safer specification. Material selection follows the same logic as any spring washer: carbon spring steel gives the best fatigue and spring performance for demanding mechanical service, while A2 (304-equivalent) stainless trades some spring performance for corrosion resistance in general outdoor or washdown environments, and A4 (316-equivalent) is worth the extra cost specifically where the equipment faces marine, coastal, or aggressive chemical exposure that would otherwise compromise a stainless spring washer's performance over time. To specify correctly, match the bore to the imperial fastener diameter and confirm the medium series is the right weight for the application rather than defaulting to it without checking the light or heavy alternatives in ASME B18.21.1's tables.

FAQs
How does a split lockwasher work?
It is formed into a helical shape from a single split ring, compressed flat as the fastener is tightened. This stores spring energy and presents biting edges at the split ends, giving some resistance to loosening.

What does medium series mean under ASME B18.21.1?
The standard defines different weight/thickness series for split lockwashers; medium series is the standard general-purpose weight, as distinct from light or heavy series options within the same standard.

How reliable is a split lockwasher for critical joints?
It provides a degree of resistance to loosening but is not considered a high-reliability locking method for safety-critical assemblies; more positive methods, such as nylon insert nuts or mechanical tab locks, are preferred where failure risk is high.