These 3-jaw, self centering feature metal bodies with plain backs. For those of you that are not familiar with chuck mounting, "plain back" means that a backing plate is required to mount the chuck to your lathe. Since there are so many different types of spindles on lathes, you would require a back plate that fits your lathe spindle and then mount the chuck to the plate. Features - Color: Silver. - Material: Metal. - Size: 4.80X4.80X3.55cm/1.89X1.89X1.40in. - These 3-jaw, self centering feature metal bodies with plain backs. - For those of you that are not familiar with chuck mounting, "plain back" means that a backing plate is required to mount the chuck to your lathe. - Since there are so many different types of spindles on lathes, you would require a back plate that fits your lathe spindle and then mount the chuck to the plate. - The mounting bolts go through the back of the plate into the back of the chuck, usually on the of the chuck since there is a scroll mechanism for self centering the jaws. - Each jaw can be adjusted separately, clamping irregular shaped workpieces can be achieved. Package list: 1 x 3-Jaw Chuck 2 x Chuck Key