A feeler gauge is a small tool commonly used in engineering to measure the clearance between to components or used within the automotive industry to measure and set the gap with in spark plugs.
A feeler gauge consists of pieces of steel at varying thicknesses, called leaves or blades. They can vary from 1mm right down to 0.05mm (very thin).
I use a feeler gauge in furniture making during a dry clamp up of a piece of furniture. I like to use the feeler gauge, normally the 0.05mm thickness blade, to feel if there are any gaps with in my joinery. If the blade slides in to the joint i know that there is a either debris on the joint face or the clamps are not pulling the joint together.
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