The Rotur Bolt Action Brass Tubes feature precision-cut brass tubes are designed to fit the Rotur Bolt Action Pen Kits and provide a sturdy and durable foundation for your writing instrument. Crafted from high-quality brass, these tubes have a 3/8" diameter and are perfect for creating elegant and durable pens that are sure to impress. The pack includes five brass tubes. Spare tubes 5 pack: PBABBT5