The Jackhammer Driving Kit (JDK) is great for large projects where the fastest installation is desired. The JDK Jackhammer Adapter Kit comes with a driving bit and HSP-T4 hammer spacer. The jackhammer bit (OH-01) fits a standard 1-1/8-inch jackhammer chuck. The included HSP-T4 works with 4×4 wood posts, the purchase of an additional spacer may be required and will be noted with each product.