Alvin - Professional Jet-Bow Speed Compass with Beam Bar - The Alvin Professional Jet-Bow Speed Compass with Beam Bar is a professional 6 inch compass with gearhead construction and double break leg design. Beam bar allows circles up to 20 inch in diameter. Features technical pen adapter and parts tube. Alvin is one of the primary sources for drafting supplies and drawing equipment in the country. Creative Coldsnow is a pround retailer of Alvin graphic arts, drafting and fine arts products.