Unusual saw

[matermark]

I think you may be referring to the little nibb protrusion? I remember seeing this subject before in one of the magazines, but I forgot what the answer was... may get many answers, from casting flash from manufacturing process, to groove starter, to anything under the sun, but wait a while to see what answers you get! The last answer I saw was you use it with a square to scribe a cut line without having to reach for a pencil!