i am looking at pics of a Schrade SC500, a 5 1/4 in. folding hunter with a button on the bolster and scrimshaw of 2 bison. searching the scrimshaw page i see a similar knife, 1979, but no button. what does the button do ? assist openning, or lock the blade open ? the only other Scrades with a button i have seen have been much older, (other than recent post of double button). so is this a 1979 knife, and were many made with this feature ? was it used on other models as well (enough to make a collection ?).thanks, roland