The Rubert 130 Composite Set Surface Roughness Comparator is a 30-specimen reference set that allows the estimation of surface roughness by both touch and sight. It covers six commonly used machining methods in a single wallet: 6 turned, 6 end-milled, 6 horizontally milled, 6 ground, 3 lapped and 3 reamed or drilled specimens.

Comparators of this kind solve a practical problem on the shop floor: they let a designer, planning engineer or inspector specify a roughness value and machining method, and let the machinist verify the finish against a physical sample of the same texture rather than relying on an instrument for every check. Each specimen is approximately 22 by 9.5 mm, and a label gives the Ra value of each in both metric and imperial units, with an Rz-value label available on request. The instruction card supplied with each set quotes the actual depth of irregularities (Rt) against each Ra value, where the Rt:Ra ratio varies from 4:1 to 10:1.

The 30 specimens are calibrated in micro-inch Ra (CLA) and in the metric equivalent micrometres Ra, accurate to within plus or minus 10 percent of the nominal values, excluding instrumentation errors. Ra coverage runs from 0.05 micrometres on the lapped specimens up to 12.5 micrometres on the milled and turned sets. The Rubert 130 Composite Set Surface Roughness Comparator measures 150 by 75 mm, weighs 100 g and fits easily in a pocket. Values follow the relevant British Standards specifications and the set is also issued with ISO 'N' numbers and Rt values. Supplied by BAMR, South Africa's authorised distributor.