A displacer is a special-purpose piston, used in Beta and Gamma type Stirling engines. The cold head contains a compression and expansion space, a regenerator, and a displacer. Usually the regenerator and the displacer are combined in one body. The concept published in 1907 has no rotary mechanism or linkage for the displacer. The ship was equipped with a "displacer", that is, a teleportation device. The hot displacer is larger than the cold displacer. Its position is synchronized with the motion of the displacer. The G40s 'G-Lader' supercharger had a displacer width of , hence the "G40" name. The engine's displacer also has very low losses. Due to its clever design the PTR does not have such a displacer. Since the displacer was chosen for high affinity, this can pose a challenge. The "40" and "60" denote the displacer scroll width in millimetres. Sometimes the displacer is specifically designed with a titratable functional group to shift its affinity.