To speed up the assembly of the stabilized remote head to the BLACK ARM by Flowcine, a second SRH Castle Nut should already be permanently placed in the mount of the BLACK ARM. To do so, a second SRH Castle Nut is need. Having a spare castle nut is always advisable, in case the original SRH-3 castle nut goes missing. Note: Metric thread For SRH-3 and SRH-360