Synonyms for T square:

n.

slide rule, triangle, Compasses, set square, plumb line, dividers, theodolite. T square (noun)
square.
gauge (noun)
level, yardstick, dial, vernier, micrometer, scale, transit, rule, calipers, protractor, rod, log, tape measure, gauge, ruler, compass, straightedge, sextant, square, line.
ruler (noun)
slide rule, yardstick, rule, straightedge.

Other synonyms:

set square, theodolite, dividers, slide rule. triangle.