Plain Flat Washers

A plain flat washer’s hardness, not just its outer diameter or bearing area, is a genuine and often overlooked specification that must be matched to the bolt or nut grade being used.

Here is why this matters. Under clamping load, the washer sits directly in the load path between the bolt head or nut and the joint surface. If the washer’s hardness is genuinely too low relative to the clamping stress generated by a high-strength bolt, such as Grade 8 or Class 10.9, the washer material can genuinely deform, or dish, and embed slightly under sustained load. This embedment is a well documented, genuine phenomenon in bolted-joint engineering, and it causes a real, measurable loss of the bolt’s actual clamping preload as the soft washer material compresses over time, even though the bolt was originally tightened to the correct torque. This is precisely why washer hardness genuinely needs to be specified and matched to the fastener grade, not simply selected by diameter alone.

A genuine, honest limitation is worth stating plainly. Because a harder washer resists embedment better, it might seem like specifying the hardest available washer is always correct. But a genuinely too-hard washer can be more brittle, and in certain dynamic or shock-loading applications, more prone to cracking rather than gracefully accommodating minor surface irregularities. Buyers should confirm both their bolt grade and the nature of the loading, static versus dynamic or shock, so washer hardness can be genuinely matched to the joint’s specific requirements, rather than assuming higher hardness is always the safer choice.

Akbar Fasteners Pvt. Ltd. exports to over 50 countries, and our plain flat washer range is manufactured and verified for hardness and dimensional compliance under our ISO 9001:2015 quality system.