I have a Pecar 4X81 scope also. At a suggestion by Mule Deer, I use Burris Signature rings with inserts to handle the 26 mm. tube. They work. Some ancient Weaver style rings supposed to be 1" also fit; but normal Weaver's, Talley's, Leupold do not.
Mine came on a rifle with 1" old Leupold Detacho rings and the tube was dented by the rings.
The scope is excellent optically in spite of it's age and the dents in the tube. I have it mounted on an equally old 270 Husqvarna with a LR FN Mauser 98 action.
WOW! just noticed how old this thread is
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Apparently the 4X81 Pecar scope was made to accommodate changing the reticle by changing the elevation/windage module. I still wonder what the 81 in the nomenclature means!