The nutsert is for either thin sheet metal or for solid material. They make two different types of nutserts. However, they do not work in wood, plywood, soft material, sheet rock, & etc. Mainly used in truck, automotive and some places on aircraft. I've sold them for the last 32 years or so. Great idea and they work great for certain purposes. Come in several different sized, metric and usa threads, fine & coarse. 6-32,8-32,10-32, 10-24, 1/4, 5/16, & 3/8".