How to say "ruler (for drawing lines)" in Arabic

Root س-ط-ر means 'to write in a line, rule paper' — a سَطْر is a line of text. That's the very same consonants as Hebrew שטר, 'document, promissory note' (a שטר is literally 'a thing written in lines'). Arabic kept the concrete tool — misṭara, the ruler you draw lines with — while Hebrew kept the written document itself.