2002 NEC, 250.53(C) Shall be connected in a manner specified in 250.70.
(exothermic welding,listed lugs,listed pressure connectors,listed clamps,or other listed means,Connections depending on solder shall not be used.
If the lug is listed for the wire property on the connection to the steal, than it can be connected to the building by the 1/4*20 screw, locknuted and torqed to the bolts manufacture standards. as long as any paint or primer is removed from the building steal first.
To insure a good connection than it would be recommended to install a min. (hex head bolt). and torqued.
A illegal connection would be with a self drilling screw...
As far as the other lug, again, as long as it is listed... (You are using for the purpose it is intended for.)
