Antique, 18k gold Trombone link chain with knot detail links in between long links with removable T Bar/extra links.
Measures 16.25in to end of T bar or 15in clasp to clasp. Links are 21.8mm long by 5.6mm wide. 18 and crown on every link as well as a difficult to distinguish makers mark and date letter (appears to be M). Weight is 43.81 grams.