yours is a 744 or 745 or 746 (4" or 5" or 6") mechanics vise. looks like a 744 from the pics. they are good vises, don't let the vise snobs say otherwise.
I've had one since I graduated that was pretty pricey at the time. if you take the slide out, there should be a month and date stamp on one of the sides. mine was made in 10/97 and I bought it in early 98. other than the chipping jaws from the powdered forged process, they are good vises and use the same pipe jaws as the 1745/1750/1755 tradesman vises. KMscott sells harden tool steel ones.