Jacks are necessary outside or anytime you have uneven ground. A level jack is a arge threaded rod with a wing nut and a welded steel plate called a base plate on the bottom. Level jacks are a must for a safe, stable, level work platform. Our jack is 24 inches in height which allows an adjustable range of 18 total inches. This allows you to locate a platform where it might otherwise be impossible. At six inches height, load rating is 13,013 lbs with a 4-to-1 safety margin. At 18 inches the safe load rating is 8,838 lbs with a 4-to-1 safety margin. See our scaffolding load test results here. Scaffoldmart carries only a solid-steel scaffold jack, not a hollow jack like some other compaine. Our wing nut is huge. It's almost 9.5 in in length. The longer the nut the easier it is to adjust it under load. We use precision square top acme threads so you can spin the nut and it spins for several seconds which shows the precision mating we have achieved with our jack. This is how we define quality. Finally it's hard to have a precision thread and hot dip it because the thickness of the zinc interferes with the precision thread. But we do cold zinc our jacks. If you need to work on unleveled ground or an unleveled rooftop consider Scaffoldmart's swivel jacks. They are very handy for working around a chimney where the roof. They are 24 inches in total length. The actual adjustment range is 18 inches of upward adjustment.