230 and adjacent a gasket 300 as can be seen in fig6 pillars 150 160 of gasket stop 100 sit below an inner surface 239 and within a slot 233 of bottom rail 230 in the embodiment of fig6 slot 233 is oblong such that retaining devices 130 140 and pillars 150 160 pass through slot 233 to an extent that projecting portions 136 146 reside along or below outer surface 238 of bottom rail 230 projecting portions 136 146 thereby retain gasket stop 100 within bottom rail 230 opening 120 of gasket stop 100 and bolt holes 222 232 of top rail 220 and bottom rail 230 respectively form a path through which a bolt or similar fastening device may be passed as shown in fig7 bolt 400 nut 410 and washers 420 430 secure top rail 220 to bottom rail 230 with gasket 300 and gasket stop 100 therebetween washer 430 is wider than a width but narrower than a length of oblong slot 233 such that washer 430 may reside against outer surface 238 of bottom rail 230 without hindering passage of projecting portions 136 146 through slot 233 the rigidity of gasket stop 100 prevents overtightening of bolt 400 and any consequent compression of gasket 300 beyond its design compression limit the thickness t of gasket stop 100 may be varied based on the maximum compression of gasket 300 desired fig8 and 9 show perspective views of bottom rail 230 with gasket stop 100.