Silver Plated Wire Guardians by Beadalon, package of 20 pieces. Hole size is .65mm or .022 inches.
Silver plated wire guardians protect all stringing materials from undue wear by keeping wire from being worn by clasps or other sharp-edged components. This size is medium which fits wire diameters up to .022". 4.5mm in length. Beading 101 - How to use Wire Guardians