Happily my PO re-did all the screens, but I've examined them. It looks like it's very small screen spline, but that's the only unusual thing about it. You can probably find the spline at a hardware store, and you can definitely find the screening material. Then it's just a question of time and patience.
Il Carriaggio — 1975 Argosy 24 | Il Progetto — 1976 Argosy 28 Center Bath | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill