Back to "skipskip"'s orginal question -- where to go for info depends on what clues the item itself provides, and where those clues take you in the mass of information you have access to.
My perspective is really skewed by over two decades editing the MVWC Newsletter, all the resources I've pulled together & in part "published" in the MVWC Newsletters, FLICKR, etc.
Just this weekend, I received an e-mail from one of the DATAMP founders which enabled me to flesh out what use was of made of an 1871 wrench patent (J.W. Mahlon patent # 118,619) & a 2nd e-mail (a query to DATAMP forwarded to me) about Alva Worden patent #415,761 which provided proof of existence of a tire bolt wrench "not previously known to have been produced."
My personal copies of Cope, Antique & Unusual Wrenches, and the back file of the MVWC Newsletters are full of notes & I have that unique "spreadsheet" which helps tie all these resources together.
Several of the members here are possibly world experts in their area of interest.
Having said all that -- these online forums are tough to beat as resources, because of the cumulative expertise they pull together.