Refers to Brodix -12 heads. They had a progression of heads from -8's on up as technology progressed in the 80's and 90's. -12 heads are a 15 degree valve angle. They also have a 12 x 12 head that is a 12 degree valve angle. They can be had with a variety of spark plug angles and port sizes. I'm sure someone will chime in with more details than I can give.