שולחן ערוך יורה דעה · סימן ח׳

English

How long must a knife be to slaughter? Any size as long as it's not too thin that it ends up piercing and not slicing like the head of a small blade or the like. And a needle, even if it is wide like those who makes holes like those who work with leather we decide with the thread. You can't slaughter with such a needle, since it is impossible to determine its size.A slaughterer with a small knife needs to be careful and measure his understanding to make sure he will not come to trample; however an extremely small (knife) we may not be allowed to slaughter with.