Good corporate directors are so hard to find that many poor souls have to serve on multiple boards.
We looked for Fortune 1000 companies where at least two board members shared board membership at another Fortune 1000 company and we found 202.
We were able to link five companies together in a sort of daisy chain, beginning with Northrop Grumman and ending with Caterpillar. The connections are shown together in the above Muckety map and step by step in the (non-interactive) gif below.
Northrop Grumman has two directors who also sit on the board of Deere. Deere has two directors on the board of 3M.
3M has two directors on the board of Abbott Labs, and Abbott has two directors at Caterpillar.
The links below will take you to Muckety maps for each crossover: