Tool one passes across? (7)
I believe the answer is:
spanner
I believe this clue is a double definition.
'tool' is the first definition.
(spanner is a kind of tool)
'one passes across?' is the second definition.
(something that spans or passes across)
(Other definitions for spanner that I've seen before include "Bad thing to have in the works!" , "Tool for gripping and turning" , "Tool for tightening or loosening" , "In the works, this tool is an obstacle" , "that might cause difficulty in the works" .)