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1. The thickness of the surface films formed during production decreases in a regular manner with decreasing roughness and with a roughness between 0.03 and 0.06 μ provides stable dimensions for gauge blocks. 2. It appears that 0.02–0.03 μ is a critical value for roughness, and that if it is decreased during lapping in building up a block, a firm and close coupling is obtained, which, however, may lead to seizing (jamming) and the formation of a cold welded seam (speedy deterioration) on the measuring surface of the gauge, and if the roughness is increased, it leads to a loss of the wringing effect and a rise in the dimensions of the gauge block. 3. The tangential resistance force may serve as a criterion of the tendency to wring. 4. A specified method of lapping end gauges should be included in the instructions for checking them.

In order to construct an inside gauge, gauge blocks and jaws are wrung together and mounted on a holder. This inside gauge is inserted into a hole to measure its internal diameter.The process of measurement consists in varying the sizes of the gauge blocks by steps of 1μ until a nice fit is obtained. By this method it takes long time to measure internal diameter precisely. On the other method, an inside gauge is constructed slightly smaller than the diameter of hole. And one jaw is kept to be contact to the wall of the hole, while other can he swung in the hole. The displacement of the movable jaw is measured by a dial gauge to obtain the internal diameter. Through the latter method, the measurement is very simple and carried out rapidly. In this report it is described how rapidly and.accurately the measurement can be carried out by the latter method.

1. A thin lubricating layer on the surface of block gauges is a prerequisite for their effective ringing capacity. 2. The thickness of this layer,under standard conditions of ringing, which provides a maximum adhesion of plates with a high grade of smoothness (13b), is constant, and equals approximately 0.01 µ. The variations in the length of a gauge block due to the lubricating layers is a multiple of their number and thus will lie within tolerances. 3. The smoother the plate surfaces are made, the firmer becomes their adhesion obtained by lapping, providing the remaining factors stay constant. 4. Friction or adhesion of plates can serve equally well as a criterion of their ringing capacity. 5. The static friction of plates under conditions of boundary lubrication follows the binomial lawf=µ(sp0+N). 6. The ringing capacity of plates is proportional to their hardness. 7. Nonpolar substances, as well as highly polar organic substances, are less effective in lapping than lubricating compounds of the type of the factory lubricant “Kalibr.” It is advisable to conduct research for new lubricants by mixing polar and nonpolar substances. 8. The firmness of adhesion between the plates is determined by the physicochemical properties of chain molecules in the lubricants, the energy of their adhesive and cohesive interaction, the peculiarities of the layer structure, and the variations of its properties as a function of the distance between the solid surfaces. 9. It is expedient to conduct research into the possibility of self-lubrication of the plates.

Two highly finished flat surfaces brought into intimate contact by a sliding action in the presence of a trace of liquid develop an adhesive bond of considerable strength in directions both parallel and normal to the interface so formed. This phenomenon has practical importance in length metrology where gauge blocks of hardened steel (often called `slip gauges') are used as working length standards. The adhesive `wringing' bond between their flat smooth surfaces is used to build up a combination or `stack' of these blocks so as to form a standard of any required length by the addition of the individual block lengths. This technique enables the combination to be handled as a single unit without coming apart but it is important to know how consistent this addition is and to quantify the dimensional effect of the `contact error' so introduced. This paper describes a series of experimental investigations which may lead to a better understanding of the physical mechanism of the wringing bond. The contact error has been estimated anew using a surface profile fitting technique made possible by the availability of high-magnification rectilinear traces of the surfaces. From geometrical considerations the minimum value that the contact error can take for two similar surfaces lies between two and four times the centre line average roughness index. The contact error variability with different liquid media, with different gauge block materials and with repeated number of wringings has been studied. The wringing forces increase and the contact error diminishes with time elapsed after wringing. High-magnification rectilinear records of the surfaces show that the surface finish deteriorates with repeated wringing by amounts which are different for different materials but which are enough to affect the repeatability of a wrung-up combination of gauge blocks. A method of contact error comparison by interferometry has been developed and this gives results which are in good agreement with the limits set by surface texture observed when fitting the high-magnification surface profiles. A tentative qualitative theory of wringing, based on the experimental work, is advanced.