There are all t-bars in my collection. From right 1st and 2nd are from Frantisek. Next is probably french. i found it on the oldest place in my favorite installation. Next is no marked and found on next building. I think it is newer than french piece. Next I found on the same wall and the same line. Next two pieces are from 1929 - 39. Righter is most popular t-bar there but last piece are wery rare. I found only one on all buildings. I must wait for bigger french piece because all bigger insulators still working.