Maker's mark perhaps N.T in rectangle and Amsterdam combined city mark and date letter 2nd standard silver ( distorted & unclear town mark of Amsterdam)
N.T in a rectangle for: Nathanael Teuter born in 1766 and active silversmith in Amsterdam registered during 1796-1831, died in 1831. He made a lot including silver clasps
Peter.
Source; K.A. Citroen Amsterdamse zilversmeden en hun merken