HIDDEN TAILOR BELT SHIRT KEEPER by Flexbelt. Keep your shirt tail tucked in with this simple under the pants belts that is made of rubber to stick to the shirt and keep it secure . Adjustable waist just like any other belt. Fits up to size 40 waist New. How it works : The hidden tailor belt is designed to be worn over the shirt tail inside the slacks. It resists the shirt from pulling up while helping to prevent the slacks from sagging down. Designed to lay flat, with the nubs facing out, when pulling on the belt, stretch it about 1 or 2 inches and push the button through any of the center holes. If the button is difficult to push through the hole, you may want to keep it buttoned, and step into it like putting on a pair of pants.