A tidy MOORE & WRIGHT 1054 standard wire gauge.

Measuring range of 1 - 26 standard wire gauge (SWG).

Marked 'MOORE & WRIGHT SHEFFIELD ENGLAND No1054 STANDARD WIRE GAUGE' with both plates stamped 'C'.

There is a small chip to one corner of the No.3 slot, please see close-up image.

Approximately 1⁷/₈ inch diameter.