This spacer has smooth bolt holes on the corners and is inserted between a surface and a split flange/flange combo, or the surface and a flange pad adapter and bolted down.  Tompkins does not offer longer Socket Head Screw Caps. The Gauge (Gage) Port Spacer comes with one (1) each of a -04 Female Flush Hollow Hex Pipe Plug (5406-FLP-04) and a -04 O-Ring Hollow Hex Plug (6408-HHP-04) so that you can plug the side that will not have the pressure gauge or line to a pressure gauge attached.  These do not come with a Flange O-ring (90DF-XX), if you need, please add onto your order.