Standard or Heavy Duty Adjustable Chain stays not too loose, not too tight Top-quality upgrade Here is a small but vital little part that we get a lot of requests for; the rear axle adjusting assembly for the Baja Mini Bike MB200 This is the piece that retains the rear axle bolt, and allows the tension on the chain to be adjusted to suit the rider Here is a small but vital little part that we get a lot of requests for; the rear axle adjusting assembly for the Baja Mini Bike MB200. This is the piece that retains the rear axle bolt, and allows the tension on the chain to be adjusted to suit the rider. Having a too tight chain is almost as bad as having a too loose chain. Either can damage your bike and spoil your day. We offer our customers a choice; you can order either one of our standard adjusting assemblies, or you can order the optional heavy duty adjusting assembly for only a dollar more. Please note that our heavy duty version is just that –heavy duty. With a