License Keys come in 4 tiers based on the number of pixel string outputs being licensed. The four options cover up to 2 outputs, 8 outputs, 16 outputs, and 48 outputs. License Keys may be stacked, but normally it would make sense to just get the higher tier, for instance a single 48-output key is best if using all outputs on a 16-port board if it has onboard ports plus differential and/or expansion board ports.