Loading Grade : Light Load Hole Diameter (OD) : 8mm/0.31 inch; Rod Diameter (Inner Dia) : 4mm/0.16 inch Free Length : 20mm/0.8 inch Product Name : Die Spring; Rectangular Section. Die springs are primarily used in die machinery.For die springs, yellow color here represents that the loading grade is light load. Additionally, we want to tell you: in the yellow, blue, red, green, brown die springs, YELLOW are the lightest load .However, because die springs are well suited for high stress applications, they are also suitable for a of other applications as well. Hole Dia: The Diameter of the Hole on the Mold ,the Outer Diameter of the spring. Rod Dia: The Diameter of the Rod that is to be inserted into this spring, the inner Diameter of the spring. Colour:yellow Material:Spring steel Package Contents: 20*Die Spring Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.