the closure member 124 is tightened the access plug 124 may be removed for donning or to allow air into the interior 104 of the shell 102 through the opening 108 the housing 110 of the access port 106 may be secured to the shell 102 by a clamp nut 132 in this regard the clamp nut 132 may define an opening 108 that threadably engages the cylindrical extension 120 of the housing 110 the clamp nut 132 may include an upper flange portion 136 having a clamping flange 138 that projects toward an outer surface 142 of the shell 102 the clamping flange 138 may have a plurality of circular ridges 140 on its face that face a clamping land 143 of the outer surface 142 of the shell 102 the circular ridges 140 may provide an even distribution of the clamping force of the clamp nut 132 against the clamping land 143 the force of the clamping nut 132 may bear against the shell 102 and the lower flange portion 112 which ultimately causes the compression of the o ring seal 118 between the shell 102 the lower flange portion 112 the intermediate lip 148 and the outer lip 114 additionally the shell lip 134 and the intermediate lip 148 may overlap and abut to provide radial locking of the device.