remove identical (imported twice, a long time ago?) threads

[sparky2]

A while back, when we imported from UBB, someone apparently imported some of the subforums more than once.

Now, in these subforums there are identical pairs (and triplets) of threads, with identical column values ( titles / dateline etc -- all same except for threadid)
-=and=-
identical sets of posts for each ot the threads
(again, all field values except the postid are identical among the duplicates)

Any suggestion as to what query I can use to select the pairs/triplets, toward using a script to remove them?