Metric Nut Identification

Fig. 2:

A nut with an ISO metric thread is marked on one face (1 Fig. 2) or on one of the flats (2 Fig. 2) of the hexagon with the strength grade symbol 8, 12 or 14. Some nuts with a strength 4, 5 or 6 are also marked and some have the metric symbol M on the flat which is opposite to the strength grade marking.

A clock face system is used as an alternative method of indicating the strength grade (3 Fig. 2). The external chamfers or a face of the nut is marked in a position relative to the appropriate hour mark on a clock face to indicate the strength grade. A dot is used to locate the 12 o'clock position and a dash to indicate the strength grade. If the grade is above 12, two dots identify the 12 o'clock position.