Why and How the gauge block can piece together
 
      The most used instruments in calibration lab is gauge block, (gage block) or slip gauge. The gauge block is the standard for length.  With such standard, once can calibration digital caliper or digital micrometer, dial indicator so on and so forth. Each block has fixed length marked on the surface. But for some purpose, the fixed length cannot meet the measurement requirement. But the inspector can piece two block together to create new length for measurement. It is amazing that the gauge block can put together. It is because the block is highly ground surface with flatness.  We call it wringing. Wringing gage blocks is the process of assembling gage blocks together end-to-end to achieve a specific measurement. Not everyone uses gage blocks in wrung combinations, but wringability can provide a test of the integrity of the surface condition of the gage block. Gage blocks "wring" together for two reasons. First, there is an adhesive action because of an ultra-thin film of oil or moisture between the blocks. Second, there is a molecular attraction, or bonding, between the blocks because of the very flat and parallel mating surfaces. Gage blocks that do not wring may give erratic and unreliable results. In fact, gage block specifications recommend replacing blocks that have lost their ability to wring.
Gage block length is defined as an interferometric measurement when the gage block is wrung to a flat platen. Airborne dirt may be minimized by keeping the gage block case closed when not in use. After being wrung, the gage combination should be placed in a covered petrie dish. Except for actual use, keep in this dish until returned to the set. Gage block wring is incorporated into the lengths of the blocks themselves, and wringing film is included in the defined length of the gage block. When gage blocks are assembled in combinations, no additional correction factor for wringing films needs to be added to the length of the combination. Wringability is an important property of gage blocks, and fortunately, it is a quality that can be controlled and monitored readily by the user of the blocks. With correct use and care, gage blocks will provide long, reliable and accurate service.
   Wringing requires two smooth, flat surfaces with surface finishes of 1 microinch AA or better. For gage blocks, it becomes difficult to wring surfaces once the flatness begins to exceed 5 microinches. The new block is suitable for wringing. Bebore wringing. There are some steps need to follow. Or it will influence the result or accuracy of block. Clean and  Remove all nicks and burrs before wringing blocks together because a burr on one block may damage the surface of the other block. Blocks may be checked for burrs with a gage block stone before wringing. A gage block stone with serrated grooves is recommended because it gives a better "feel" for nicks and burrs that catch the edges of the serration. Badly nicked surfaces will click as a nick passes along the serration. So. When you use the blocks, avoid to touch the measuring face and using gloves instead of touch the blocks by hands directly. never allow a gage block combination to remain wrung up more than one shift. We have found that blocks left wrung up rust very rapidly. Before returning the gage block combination to the case, the blocks should be cleaned with a fast-drying solvent and dried with lint-free cellulose tissue.
   
Disassemble the block
1. Turn them first at right angles, then slide one off the other. Do not apart them directly
 2. Blocks should not remain wrung together overnight, or separation maybe difficult.
 3. Once apart, Clean the block and oil. Do not touch the measuring face. Then put them back to the case.