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Qualfast M45X1.50 Hex Thin Nut (4)
Hexagon Thin Nut, MF (Metric Fine), Steel - Standard (Self Colour), Plain - Grade 4, DIN 439 B (1987).
https://www.bizrate.co.uk/homehardware/qualfast-m45x1-50-hex-thin-nut-oid27752519877.html