This PTFE holder is used to hold the Wilmad microcells secure. Fits into any Wilmad 5 mm thin-wall sample NMR tube, 506-pp or higher quality. The top portion of the holder which takes the positioning rod has an I.D. of 0.1655 +/- 0.0005 in. The lower end (blind hole) which holds the stem of the sample tube has an I.D. of 0.058 +/- 0.001 in.