The "plus" in the OB-250+ is the ultra-premium JLS #12 tone ring. Developed by master caster Jim Stull of San Antonio, Texas, this ring is the result of years of analyzing many pre-WW ll G-word tone rings to ascertain the formula of the bronze alloy used to make them the sought-after pieces of hardware they've become. This long-skirt tone ring improves the contact between the neck, the rim and the tone ring, increasing the transmission of energy from the pot to the neck. It mimics the tone of the costly originals at a tiny fraction of the original's cost. The OB-250+TP adds the phenomenal Tony Pass/Schaefer birch (recovered from the bottom of Lake Superior) block-style rim for even MORE powerful tone. Includes hard shell case.