Alwan Canson T-Square Head Replacement, Blue

A T-square is the tool that guarantees a horizontal line. Its head hooks over the straight left edge of the drawing board and slides up and down, so every line drawn along its blade is parallel to every other — and a set square resting on the blade gives you true verticals and angles from the same reference.

The head is the part that wears and the part that decides accuracy: if it develops any play against the board edge, every line drifts. This is a replacement head, sold on its own so a good blade need not be thrown away when its head loosens or cracks. Fit it square to the blade and check it against a known edge before trusting it — a head fitted even slightly off throws every line by the same error.

An Alwan Canson replacement head in blue. Buy the head that matches your blade thickness — a head cut for a thinner or thicker blade will not clamp square, which defeats the point of replacing it.

• Replacement T-square head
• Restores accuracy without replacing the blade
• Fit square to the blade and check before use
• A loose or off head drifts every line