Replacement Nitro Start backplate for the Savage X with F4.6 engine.To use this backplate, your F Series engine must be fitted #15136 STARTING SHAFT (NITRO START F SERIES)Use with the following Starter Unit and Starter Shaft:#87630 - HPI NITRO START SYSTEM (STARTER UNIT) #87617 - HPI NITRO START STARTER SHAFT (280mm)See below for kit compatibility.