Tough-Spots, 3/4", White, 500/rl Fits 15ml Tubes 3/4" Spots Pre-cut Round Labels For Microtube Cap or Lid ID Freezable in Liquid Nitrogen Autoclavable/Boilable Chemically Resistant Won't Dry Out, Fall Off or TearShipping Weight: 0. Tough-Spots are made of a special smear resistant material and will accept any marking instrument.50 x 3.50 x 1.