Unfortunately I'm old enough to remember, they were mounted in an oblong frame that slid into the keyways at each side of the viewfinder, in common with the FTb EF and A1 and some the other FD cameras, except the F1 and T 90 that were different.
Photrio.com contains affiliate links to products. We may receive a commission for purchases made through these links. To read our full affiliate disclosure statement please click Here.