The Bilstein 5125 Series KBOA 550.50mm is a gas-charged monotube shock from the B8 5125 line, which the manufacturer positions for custom builds and vehicles without a direct Bilstein fitment. Its 46mm digressive piston uses self-adjusting deflective disc valving, so damping responds to surface changes rather than sitting at one fixed setting. For a lifted truck or a rebuilt off-roader that outgrew its stock shocks, that valving and the high-pressure monotube design are the main reasons to pay more than a budget universal shock.
Fitment is where careful buyers should slow down. This is a universal-length unit, not a bolt-in part, so measure your eye-to-eye length at full compression and extension and confirm the application with the manufacturer before ordering. Owners on user forums report that the 5/8-inch eyelets on universal 5125 units sometimes need swapping for 14mm bushings on certain trucks, and that stock upper mounting points can call for custom washers or bushing work. Searchers looking for a 46mm monotube eye-to-eye lifted truck shock, a universal Bilstein 5125 rear shock, or a 550.50mm extended-length Bilstein will find this part matches that profile. Warranty terms for the series are published inconsistently, so confirm coverage directly with the manufacturer.
The manufacturer describes the B8 5125 line as designed for custom applications and for vehicles without a direct Bilstein fitment, so it is not a plug-in replacement for most trucks. Measure your eye-to-eye length and confirm the application with the manufacturer before buying.
Owners on user forums report that the 5/8-inch eyelets on universal 5125 units sometimes must be replaced with 14mm bushings and hardware to fit certain trucks. Check your existing mounts before ordering.
Published warranty terms for this series vary. Confirm the exact coverage with the manufacturer before purchase.
The manufacturer has not published a difficulty rating for this specific part number, so plan around the mounts you already have. Owners on user forums suggest test-fitting the bushings and eyelets on the bench before raising the truck, since mismatched bushing sizes were the most common snag. On some one-ton rear applications, owners report a 9/16-inch bolt where the shock uses 1/2-inch hardware, which they solved by removing the shock sleeve or welding washers to the mount. Front installations on a stock upper mount may also need a custom insert, so have a lathe-turned bushing or spare hardware on hand.
