The full Starrett combination set with precision ground cast iron square head, centre head and reversible direct reading 180º protractor.
Both sides of the 300mm hardened steel blade are engraved with full mm on one edge and half mm on the other, the rule is flippable and (by reversing the retaining clip) reversible, so you can get either whole mm or half mm, ascending or descending, from any of the four corners of the face.
The reversible protractor has a broad foot with a slot down the middle for the rule, so it can register from either face / edge of the work, (non reversible protractors only have the foot on one side) both are read from one side.
The centre finder is also designed to be used independently as an internal square, the apex is relieved to allow for burrs on the corner of the work. With the blade inserted it can reliably find the centre of round or near round objects up to 40cm in diameter.
The square head incorporates a spirit level, which because it's on a square also gives plumb, with accurately precision ground faces at 90 and 45 for the obvious use, and a scriber screwed in at one end, not quite as nice to use as a proper scriber, but it's always to hand as a back up. The square and centre heads are ground to the same thickness and lie flat on both sides, so they can be used to elevate a workpiece to clear a protruding feature. Because the rule slides it can be set to a given length for go / no-go measurements or used as a depth gauge.
The heads on this version are cast, denoted by the crinkle finish. Cast heads are more dimensionally stable, forged heads are stronger, we have never heard of anyone breaking a Starrett cast head.
Although there is no current standard for combination squares, Starrett continue to manufacture to a now obsolete U.S. federal specification of 0.004in per foot max deviation between the square head and the blade, 3 minutes of a degree max deviation for centre heads, 15 minutes of a degree for protractor heads with blade edges straight to 0.001in.
All standard Starrett combination set components are interchangeable, (Laroy Starrett was inspired by the working standards Samuel Colt in this regard and it has been retained ever since) so if you decide after ten years to add a longer rule for example, you can be confident that everything will still work together with no loss of accuracy.
Packaging: Fitted Foam Lined ABS case