I'm sure Rapid could answer that. However I think that it would be no problem to put LEDs 2" on center, which is what I have been doing. I have a 8.5" x 6" heat sink with 7 LEDs, 2 rows of 3 in a rectangle all 2" apart with one blue in the center like a capital I. That heat sink gets warm to the touch but never too hot to grab and fiddle with. So you could probably put 2x that on the 10" wide one and still be OK but I would be putting either 8 or 10 on it.