The 51 pattern is a 4" lock-back knife that was manufactured from the late 70's to the early 90's. They have a single blade that will be either a skinner blade or a clip blade that locks open. Because of this they will have an L following the pattern number. When the master blade is a clip, the knife will have a 1/2 following the pattern number as well.
If the s's on the blade tang are lightening shaped, and the dots are located between the Case XX, and the U.S.A. that would put the date at 1982. Not particularly valuable but a nice knife....enjoy !
The walnut handle materal was used on Case's more inexpensive knives as it was cheap, easy to work with and very durable. It was often used on their electrician's knife.
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