We recommend an additional (4) sets of letters with the NTRB3, (3) with the NTRB2, and (2) with the NTRB1. Sets include the following quantities of 3/4" letters, numbers and characters: A/15, B/9, C/9, D/9, E/21, F/9, G/9, H/9, I/12, J/3, K/6, L/9, M/9, N/9, O/21, P/9, Q/3, R/12, S/15, T/12, U/9, V/6, W/9, X/3, Y/6, Z/3, 1/6, 2/6, 3/6, 4/6, 5/6, 6/6, 7/6, 8/6, 9/6, &/3, ?/3, ,/3, -/3, ./6, $/6.