Rotring T-Square Head, Red

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.

A rOtring replacement T-square head in red. rOtring is the technical-drawing name many Egyptian drawing offices standardise on, so if your blade is a rOtring this is the matching head — fit and thickness cut to the same blade rather than approximated.

• 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