Here is what you need to do. Measure from the center of your highest string to the center of your lowest string. Lets say it is 3.75 inches on a 6 string. You will need to divide this number by the number of spaces between each string. In this case there are 5 spaces. So if the string spread is 3.75, we divide that by 5 and we end up with a string to string spacing of .750.
Aluminum bridges are lighter in weight so if you are concerned about your instruments over all weight than aluminum is the way to go. Aluminum tends to deliver more mids and highs while brass accentuates the low end tones.
Yes, all of our A style bass bridges are string thru, please specify when ordering vintage or B style bass bridges so we can accommodate your requirements.