A union is a fitting that allows a threaded joint without requiring the joined pipes to be rotated. They are usually made of either steel, brass or PVC. Most unions are pressure rated. A union consists of two female threaded pieces, connected by a threaded oversized nut. The pipe couplings are either socket-weld, capillary (for brass) or threaded. PVC unions have been known to blow up when used in hybrids, Boogieman and LuckyThirteen13's PVC unions have exploded before. Variations on the union exist, like 90 degree unions. Alternatives to unions include flanges and camlock couplings.