24 Inch Stainless Steel DCP Extension Rod can be used with both Threaded and Quick Connect style Drive Rods. Typically these are used with the 12" Drive Rod (DM.QC.5 & DM.THD.4) and driven in approx 24" then another 24" drive rod is attached and the test can continued. Care must be taken but this allows for greater test depth. We also sell kits for both styles that include (3) 24" drive rods and a 12" adaptor that allows for a 7 foot test depth.