To meet the demands of oval track racing, KONI has chosen the Mono-tube gas charged design. This technology provides no fade valving and enables mounting of the shock absorber upside-down, lowering the unsprung weight of the vehicle. Key features include a large 46mm diameter piston (velocity sensitive); Lightweight single wall body / fewer internal parts; Consistent no fade valving / separate gas chamber; New low gas pressure for better driver feel. Some other manufacturers place a plastic bag filled with gas inside a hydraulic twin tube shock absorber, as a means of preventing aeration or free stroke, when the shock absorber is mounted upside down. In theory this is logical thinking; however, in practice the plastic bags usually fail, resulting in aeration and reduced performance. The plastic bags are not heat resistant and float within the shock absorber. The bags fail prematurely because of the abrasions received as it floats within the cylinder, and the high operating temperatures experienced in oval track racing. When mounting a shock absorber upside-down, the only shock absorber design that will not fail under the extreme conditions of oval track racing is the Mono-tube design. Lacking the engineering and manufacturing sophistications of KONI, other suppliers offer the "gas cell" or plastic bag design. KONI's 30 Series Steel Body Shock is a single adjustable mono-tube design. There are four distinct rebound adjustments that allow you to adjust the shock to suit your needs, chassis set up, and track conditions. It is lightweight, very consistent, and affordable. Use with Coil-Over Kit #KON30-0000 (sold separately).Pit Stop USA offers Koni 30 Series 4 Way Adjustable Steel Body Mono-Tube Shock - 9" Stroke - Compression (3) 70#, Rebound (2-5) 345# - 405# - 495# or 630# 30-9325 at low everyday prices. Be sure to check out all of our products from Koni Shocks including Koni Shocks 30 Series Adjustable Steel Body Shocks.