I recently purchased a set off these to replace the broken axle centers in my Bachmann SP 4-8-4 #4449 product #11301. I was thrilled to even find they exist. Parts for these pancake, split-chassis, or sandwich chassis designed engines (of which many were produced) are no longer available. The original axle centers or couplings split open and engines like this are made inoperable in the process. My Rickman parts arrived Tuesday and I installed them last night. So far they're working and hopefully they will last, but there is one bit of feedback I would like to provide as well as see if others have experienced or possibly worked on themselves. The teeth of the gear printed into one of the four centers are more like lobes than teeth. I think it would help if they were made a bit deeper or more definitively as teeth. There is inference between this gear and the one it meshes with. You can hear noise from them meshing and vibration is emitted from their interaction into the tracks. It sounds as though the tips of the drive gear in the engine are striking the bottom of the teeth or lobes of the Rickman gear. If the Rickman gear teeth were a bit deeper I think they would mesh better with the drive gear the engine would run a lot quieter and smoother, and this set of centers could become the ideal set of replacement parts that it has the potential to become. (Assuming they last.) Otherwise, I'm just grateful to DK for having produced these at all. I'm tempted to tell a lot of others with HO engines rendered useless by their faulty original parts about this set of replacement parts, but would prefer first to see if there's a way to resolve the gear gnashing noise and vibration. See photos below - sorry about the lack of good focus on the original Bachmann axle-center gear and that I didn't yet clean it yet, both would have helped call out the depth of its teeth by comparison. But hopefully you can see what I mean.