The gasket 18 is then positioned on the active surface 16 of the substrate so that the central opening 19 in the gasket is fully within {TAIL ~ the window} opening 21 of the base at a proper position, and the press block 13 is then positioned over {HEAD ~ the gasket} 18 so that the engagement surface 20 properly seats against the gasket 18 
The gasket 18 is then positioned on the active surface 16 of the substrate so that the central opening 19 in the gasket is fully within { TAIL ~ the window } opening 21 of the base at a proper position , and the press block 13 is then positioned over { HEAD ~ the gasket } 18 so that the engagement surface 20 properly seats against the gasket 18
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