Gaskets and seals are both designed to prevent leaks, but the two products perform somewhat differently. Mechanical seals function in rotating machinery and are typically integral parts of the machinery. Gaskets are more static, even if they are form-in-place gaskets or joint sealants. Gaskets need to be fitted to the sizes and positions of the bolts that extend through them, but are easier to replace even if they are customised for a particular function or machine. Some mechanical seals are easily replaceable, but many of them need to be repaired or reinstalled if they break down, often together with the machine itself.