For future reference, the ISO standard specifies two standard tripod threads - 1/4"-20 UNC and 3/8"-16 UNC. If, as is likely, your Velbon tripod has either of these then there should be no problem mounting heads from other manufacturers.
Not quite so simple, some tripods have the female socket on the head and the male bolt stem on the tripod, others are vice versa. So there's a lot of permutations. Ian