Good question! Usually less than you might think. The grips need to penetrate the material to really work best, so if you use too many, the increased surface area of the grips may not allow them to penetrate with the force available from your vise. If you have to use a cheater to get adequate penetration then you are likely using too many. Most single parts can be clamped really well using two grips per side. Some small parts can be clamped using only one grip per side. Larger parts may require up to 3 grips per side. If properly spaced and you have good penetration 3 grips per side will allow some pretty big parts to be machined very aggressively. You will be amazed at how well they hold!
