Use a fully assembled pack to check battery fitment while sanding. A single cell will not tell how the full pack is going to sit in the slots as a single unit. Your best bet is to have one pack that is perfectly assembled (preferably from a good battery jig) that sits flat on the table - no rocking or air gaps or warps, to check the slots with.
Speed Merchant Rev7, Tekin, TQ Racing (wire), Team Tamale
RC Excitement - Buy where you race, support your local tracks.