Triangles are essential tools for manual work.  Two triangles are required: a 30-60-90° and a 45-45-90°.  A small size (4 to 6 inches) is convenient for students. The two triangles can be used with the T-square to produce vertical lines or lines at 30°, 45°,  or 60° to horizontal.

Triangles are used with the T-square and with other to make vertical and angled lines.

The triangle can be used together to produce angles at 15° increments.

Triangles can be used together to make angles in any 15 degree increment.

Triangles can also be used to draw parallel lines, but this will be discussed later.