A bar gauge greatly reduces the chances of error by enabling you to directly compare or transfer dimensions. It is very useful for example when testing a drawer for squareness by checking that the diagonals are equal. The bar gauge base unit consists of two 150mm steel rods fixed to aluminium clamp heads. The rods have threaded end holes that accept interchangeable brass tips or extension rods (included). Three styles of tip are included: ball tips for inside measurements, pointed tips for inside corner measurements and mushroom-shaped tips to hook over edges for outside measurements. The distance between the ends of the round or pointed is equal to the distance between the inside faces of the mushroom-shaped tips. This lets you convert an inside measurement to an outside measurement just by switching tips. The base unit adjusts from 183mm to 305mm. Two pairs of extension rods are included, 100mm and 305mm, allowing a maximum span of 1,118mm. For greater reach, additional 305mm extensions are available. Made in Canada.