This is an angled mortar rack, with 1.91 ID x approximately 15 inches long mortar tubes with wooden plugs in the bottom of each. Use these for consumer festival ball shells (reloadables) which are 1.88" in outer diameter or smaller. IMPORTANT: If your shells are smaller than 1.75", use TU2100 spiral cardboard tubes. Firing too small a shell from too large a tube can cause a low-break. Low breaks can cause personal injury or fires being started. ea.