Abstract: A mounting plate is used to install any optional accoutrements or attachment on a linear motion guide unit. The mounting plate is made of a molded product which is inexpensive in production cost and easier in its accurate conjunction with a slider to get the attachment bringing out the best in function. The mounting plate is made to have surfaces opposite to each other, one of which is a first mounting surface inward coming into mating with the one end surface of the slider and another is a second mounting surface outward coming into mating with the attachment. The mounting plate is made of a molded product. The mounting plate is made of an injected mold product of synthetic resin which is composed of a major part of synthetic resin and a metal core centrally embedded in the major part.