Reduced Loadability of DIN compared to ISO Nuts
Dr Bill Eccles
Some years ago, on a Bolt Science training course given to largely Design Engineers at a major manufacturer, they spoke about a thread stripping issue they had on one application. The nuts were stripping, and they didn’t know why. Looking at the nuts they had a |8| marking on them, they had assumed that they were property class 8 to the relevant ISO standard (which is ISO 898 Part2). They thought that the vertical bars at either side of the 8 was just decorative and of no significance. In fact, they are essentially a separate property class, property class |8| to a withdrawn DIN standard. Such nuts have what is referred to as reduced loadability, the nut’s proof load is lower than that of an ISO nut. The reduced strength of the DIN nut was a likely cause of the thread stripping issue that they were experiencing.
Many of the modern fastener ISO standards were developed from original DIN standards, with the relevant ISO standard subsequently superseding the DIN standard. Effectively, the DIN standard becoming frozen at its last update. For example, August 2023 celebrates the 40th anniversary of the last update of a standard that is still used today in the manufacture of millions of nuts. In my experience most Engineers are unaware of the reduced loadability of DIN nuts when compared with nuts manufactured to the latest ISO standard. That is, they are unaware that they are weaker and more prone to thread stripping.