Domestic and portable recorders used inch reels (or spools). Another explanation is that it refers to "spools" or reels of magnetic tape. Some machines produce very long pipe cleaners which are wound onto spools. Tape spools were usually made from transparent plastic but metal spools were also used. Two spools needed more knowledge about bearings and sealing. Some are larger than knitting spools, and can knit larger items. Other tools such as knitting spools or pom-pom makers are used to prepare specific ornaments. These medium format cameras used 120 film rolled onto spools. Large numbers of clay and stone incised spools and whorls attest to local cloth-making. There are 70,000 microfilm spools of both Danish and foreign newspapers. A high pressure ratio along with contra-rotating the IP and HP spools improves efficiency. A turbocharger serves to supply engine boost and spools up the passive turbocharger. British gunsights, catapult spools and other items were installed. Histones act as spools around which DNA winds. Turboshaft engines are sometimes characterized by the number of spools.