Oz-Post model ISW-850 and IS-600 are designed for the 2 3/8 outside diameter round post. The main difference in these two posts is the overall length of the Oz-Post. As a general rule, if you can dig a hole 2-3 use the ISW-850. When soil conditions are very hard and rocky and it is difficult to dig 12 use the IS-600. This post is ideal for fencing and sign posts and is one of the most popular Oz-Post models. These models are designed for standard fencing that is 6-7 high with post spacing of 8. For 8 tall fencing the post spacing should be 6 which is standard practice for alternative post installation methods. It is recommended that the ISW-850 be used with all 8 tall fencing. The ISW-850 includes a compression collar that secures the post to the Oz-Post. Unlike the square Oz-Post models that use screws for connection, the compression collar slides over the round post and is locked onto the Oz-Post. The compression collar is easily installed using the Cap Driving Tool (see additional information in the product listing of this website). The compression collar may also be installed using a hammer or larger piece (3 round) of steel tubing. The compression collar is removable if the project is for temporary purposes. When installed as recommended the connection will provide you and/or your customers with a strong foundation for your construction project. There are several options for installing this post, these options are explained in the how-to instructions of this site. To summarize, you can leave the top sleeve completely above ground, half in half out (recommended) or completely bury the top sleeve out of sight. When burying the sleeve completely be sure to make sure the sleeve is clear of dirt to get a firm connection with the post. There are grooves at the bottom of the sleeve that grip the post so it is not able to move once the compression collar is installed. Regardless of what you plan to build with Oz-Post you can be sure that your post will be sturdy. INSTALLATION: Option 1 Jackhammer: use the Oz-Hammer model OH-01. No spacer is required with this model. Jackhammers are easy to operate and available to rent at all rental centers in the country. Oz-Post recommends an electric or gas powered jackhammer. Pneumatic jackhammers are also ok but they are often much heavier and unnecessary. Option 2 Sledgehammer: cut scrap piece of material about 8 and insert into the top sleeve. Strike the material with the head of the hammer to drive the post into the ground. HINT: Be sure that the scrap piece is a loose fit so that it is not difficult to remove after the post is installed.