Unless the blades have a cradle, you should DEFINITELY not be using a washer between the two.
http://www.lawnsite.com/archive/index.php/t-35088.html

Mower 2 includes a cradle 72 for releasably receiving battery 7 . Battery 7 and cradle 72 have plug in connectors (not shown) such that battery 7 automatically connects to the electrical system of mower 2 when it is dropped into and seated within cradle 72 .
http://www.freepatentsonline.com/7111443.html

These mower are really no different than a conventional lawn mower except the frame and decking are reinforced with extra thick steel, a small cradle for the battery
http://www.funmower.com/faq.html

A special cradle makes the large capacity grassbox easy to roll on and lift off without spilling the grass clippings.
http://www.gardenequipmentdirect.co.uk/#/atco-royale-mowers/...

18. The mower of claim 17, wherein opposite ends of the cross frame have upwardly extending cradles that further connect the cross beams, and wherein each motor is secured to a cradle on each end of the cross frame.

Read more: http://www.faqs.org/patents/app/20090183479#ixzz0kMFQME2L

Improvements to presses for the pressing of scrap in skips which charge furnaces in steelworks, whereby a skip (l2) is borne on a support with legs (l5) by means of a vehicle with a vertically movable platform (l6) and is then rested on a press cradle (l7),
http://v3.espacenet.com/publicationDetails/biblio?CC=EP&NR=0...

see Fig. 2, item 17
http://v3.espacenet.com/publicationDetails/mosaics?CC=EP&NR=...

All these cradles have one common: to support or hold a part by another.