In dissolution testing, the U.S. pharmacopeia allows, as a variation to Apparatus 2, a non-reactive stainless steel wire helix as a 'sinker' to be typically used to sink dosage forms that would otherwise float. The objective of this investigation was to determine if other sinker shapes will influence the rate, extent, or variability of dissolution. Criteria for the optimal sinker were defined. Various new sinker designs were fabricated, tested, and classified.

Four classes of sinker shapes were defined:

Longitudinal sinkers contact the dosage forms on the long axis. Lateral sinkers either wrap around or contact capsule dosage forms in the middle, such as the line where the top and bottom halves of a capsule shell come together. Screen enclosures are of two types: either a wire cage, which holds the capsule, or a circular piece of wire screen placed on top of the capsule. Internal weights consist of two steel ball bearings, one inserted into each end of the capsule.

The choice of sinker will depend on the tablet or capsule.
In general there are some guidelines that can be followed however:

Japanese Sinkers are specified by the JP and have strict dimensions.