Chevrons. I should have remembered the correct name... being an ex P.O., Sea Cadets. The correct name is the iis the 'Good Service Badge'.
Here is the following:
3921. Good Conduct Badges Good Conduct Badges are represented by V-shaped stripes, 12.5mm in width at the perpendicular and 127mm across the top of the V; they are worn on the left arm by entitled ratings below the rate of Chief Petty Officer. When worn without a rate badge, the centre of the device is to be midway between the point of the shoulder and the point of the elbow. When more than one Good Conduct Badge is worn, the distance between them at the perpendicular is to be 12.7mm.
Stephen