The Standard Platinum Resistance Thermometer (SPRT) is defined by the International Temperature Scale of 1990 (ITS-90) as the interpolating instrument for temperatures between 13.8033 K and 1234.93 K. This SRM concerns the calibration characteristics of a group of 20 capsule-type SPRTs within the range of temperatures between 13.8033 K and 429.7485 K. The platinum wire used for the construction of the resistor elements of this SRM was derived from platinum bar stock with a chemical purity of 99.999 % by weight. Each of the 20 units has been evaluated, certified, and calibrated according to the definitions of the ITS-90. The resistance characteristics of all 20 units have been measured at 11 fixed point temperatures from 4.22 K to 429.7485 K as well as at least 7 other intermediate points. The procedures used in performing the calibrations and the supplemental measurements are documented in this publication. The resulting analysis pertaining to each individual unit, as well as the SRM sample population as a whole, is presented in detail.