Health What is the function of test tube clamp? What is the function of test tube clamp? This test tube holder, or clamp, is 6.25 inches long with finger grips. Holds any size test tube. The test tube holder is used to hold test tubes when they are hot and untouchable. Related Posts:Are tube amps durable?There is a guide to standard sofa sizes and dimensions.Can I wear diamond ring on my middle finger?How long will a tube amp last?