These 9 mm thick internally and externally threaded polymer rings are to be placed between an objective and nosepiece to inhibit thermal conductivity.

It is recommended to add spacers to other objectives on the nosepiece for parfocality. Available in three formats: for RMS, 0.8"×36 tpi, 25 mm for 25×0.75 mm objectives, or 27 mm for 27×0.75 mm objectives.