Optionally, longboarders add bearing spacers between the bearings in the wheels. Neoprene joist tape or u-shaped rubber spacers help decouple the subfloor from the joist. Each rail has a series of pins with rubber spacers that support the bars. The thickness of the air spacers may be determined as shown in Fig. This consists of interchangeable structural spacers that extend the headtube's height. This used two frames held in parallel with spacers. The Ambassador received minor changes, such as small chrome spacers on the cowl air scoop. Further the buttstock can be lengthened by adding spacers. The timbers may be stacked with spacers (known as "stickers") between them. There are secondary features which emerge from the gaps between spacers after further patterning. Certain archaeal viruses were shown to carry mini-CRISPR arrays containing one or two spacers. In prokaryotes, CRISPR are arrays of alternating repeats and spacers. The repeats are separated by spacers of similar length. Prostheses come in many varieties, such as spacers or resurfacing prostheses. Often the handle is made from various materials between spacers.