~32 HO inch Manhole Covers

These are something I made for my own modelling.  The fine print says City of Vancouver Sewer, but it does not render using Shapeways Frosted Extreme Detail material, so these end up looiing like large size generic manhole covers.  They were scaled from actual covers in town here, then very slightly enlarged to better fit 3/8" diameter.  Each cover is like a small button on the sprue.  there are 8 on the sprue.
I finish them using a dark grey/rust brown paint mix.  When that dries, I rub the top surface with a pencil to give the appearance of burnished iron.  
Install by drilling a 3/8" hole into the road surface; the depth must be enough to nest the button to a flush mount in the road surface (I usually drill overly deep, as too deep isn't a problem).  When drilling the hole, use a sharp bit and strive for a true vertical motion to create a uniform hole.   I use a little clear adhesive caulk to fill in the bottom of the hole if it is too deep, and a trace/little caulk around the edges, as glue for the button.  Then carefully insert the button and use finger pressure to push it flush with the road surface.  Carefull not to push it in too deep.  If you get it in too deep or tiped at a funny looking angle, use a pencil tip to tilt it down on one side.  The other side will tip up and can be grasped with your tweezers.
Good luck & and happy modelling.