Spring Diameter


             When engineers talk diameters of springs there are a couple different categories with several different uses of terminology.  First, wire diameter is the size of the raw material used in coiling and it is often called bar diameter as well.  The size of the material is very important to the design as well as the forces. Moreover, it designates which machine has the capacity to run that size wire, and also which wire line tools to use when manufacturing parts in that machinery.  If your tools are not the correct size the wire will slip or destroy your valuable tooling. 


Outside Diameter, Inside Diameter and Mean Diameter all relate to the body of your spring—if applicable.  Most extension, torsion and compression springs have a body that will be critical for accomplishing the correct forces.  When it comes to a physical spring we almost always measure diameter as an outside diameter with calipers or sometimes an inside diameter using gauges.  Gauges are very important because if a spring is in tolerance at an inside diameter of .500 +/- .030 you can simply put .525 pins and .475 pins on the gauge.  If .525 pin fits you may be approaching trouble, if the .475 pin does not fit you may also be in trouble and in need of an adjustment.  Maintaining your diameter with a quick check procedure is critical to our lean manufacturing principles.  There are relationships between all of these diameters where if you have one you can find all the others.  From an outside diameter you can subtract one wire size to find the mean diameter and two wire sizes to find the inside diameter and vice versa.  This is critical when moving a design from the engineering process into the manufacturing process because spring technicians need tangible measurements that they can easily measure on the go.