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Fig. 35 
GX, GY and GZ gauges; A, 5ix piston holes, 1/2 inch diemeter; 
B, self-centreing steel washer, overlepping all the piston 
holes 1/32 inch; C, eyebolt; the anvil face is 1.3 inches from 
the bottom of the gauge; D, annuler air-chamber, 5/8 inch from 
top to bottom, 13/32 inch from inner to outer radius; this 
chamber communicates with the space below the anvil by six 
tunnels, 1/4 inch diameter, which are staggered between the 
piston holes; E, eperture, 1/8 inch diameter, for admitting 
water to the air-chamber. The foregoing dimensions refer to 
the GX gauge, which is shown in the figure; the GY end GZ 
geuges are similar but longer, differing only in the following 
dimensions--in the GY gauge the air chamber is 7/8 inch from 
top to bottom and the anvil face is 2 inches from the bottom 
of the geuge; in the GZ gauge these two dimensions are 1 5/8 
inch and 3 inches respectively. The pistons used in the GX 
gauge are 3/4 inch or 21/32 inch long; in the GY gauge 1 11/32 
inch or 1 5/32 inch; in the GZ gauge 2 1/8 inch or 1 5/8 inch. 
Except as regards length, the pistons are similar to those 
used in the G gauge, Fig. 34. 
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Fig. 36 
GA and GB gauges; A, three piston holes, 1/2 inch diameter; 
B, three pairs of steel washers (No. 0 BA), each pair posi- 
tioned to overlap two adjacent piston holes 1/50 inch; 
C, eyebolt; the anvil face is 5 1/2 inches from the bottom 
of the gauge; D, annular airchamber, 3 5/8 inches from top 
to bottom, 5/16 inch from inner to outer radius; E, three 
air tunnels, 5/16 inch diameter, staggered between the 
piston holes, connecting the air chamber with the space be- 
low the anvil; F, aperture, 1/8 inch diameter, for admitting 
water to the air chamber. The foregoing dimensions refer to 
the GA gauge, which is shown in the figure; the GB gauge is 
Similar but longer, the air chamber being 9 inches from top 
to bottom, and the anvil face 10 3/4 inches from the bottom 
of the gauge; also, in the GB gauge, the air chamber has a 
central flange to guard against collapse of the outer wall 
under strong external pressure; this flange is mutilated to 
give ample air connexion between the upper and lower halves 
of the chamber; the pistons used in the GA gauge are 4 1/4 
inches or 3 inches long, in the GB gauge 8 3/4 inches or 
6 1/4 inches. 
