American Wire Gauge (AWG) insulating tubing is size specified by its inside diameter (ID). This differs from pipe and tubing used in fluid handling applications where size is specified by outside diameter (OD). Since AWG sized tubing is used primarily as electrical insulation, it is only logical that ID is the critical measurement. AWG sized insulating tubing is not usually pressure rated. The smaller sizes of this material are often referred to as "spaghetti", while the larger sizes are sometimes referred to as "macaroni". Spaghetti and macaroni are manufactured in a wide variety of materials with vinyl tubing being perhaps the most common, but in the well logging industry, Teflon tubing is most commonly used. Occasionally silicone, silicone coated or impregnated fiberglass, or other exotic tubing will be found inside well logging tools.
Extruded Teflon (polytetrafluoroethylene or PTFE) tubing is wonderful stuff; you cannot hurt it with a soldering iron. If you are accustomed to fighting insulation melt-back with ordinary PVC or other low temperature tubing, you are in for a treat when you try Teflon. Teflon tubing has been used in downhole logging tools almost exclusively since the 1960s because of its excellent high temperature performance. Some manufacturers have also used it in logging surface electronics. Teflon insulating tubing is available in a wide variety of colors, nearly as many as for Teflon wire, but the translucent white, often referred to as "natural" is the most commonly found in the marketplace. AnaLog Services, Inc. uses Teflon tubing for all well logging electronics applications where insulating tubing is required.
Applications for Teflon tubing in well logging tools include both those primarily intended to provide electrical insulation (as in component lead insulation), and those primarily intended to provide mechanical protection (as in lead wire protection in CCL applications). #4 tubing, usually in thin wall construction is used to insulate 10-32 threaded rod contacts many places in logging tools. Some sinker bars require #5 thin wall tubing to insulate their contact rods. #16 tubing works well for extra insulation or for mechanical protection when slid over 24 E, 24 EE, or 22 E Teflon insulated wire (it is usually very snug on 22 EE). Many shooting CCLs use #16 Teflon tubing to protect the coil lead wire, and
Bell used it to provide extra insulation for the very long high voltage supply lead wires in some of their radiation tools.
The table below summarizes dimensional data for Teflon tubing, and comes principally from Zeus.