I know this was covered somewhere before, however I thought I would post my DIY solution
I got the spikes (nut covers) from Iowa 80 truck stop. They are also available online http://www.iowa80.com/DirectionsWEB/webcart_search.php?scr_searchArg=spike&cart_truckType=
I used the 9/16 th for this. (.89 ea)
Part list from Home Depot
1 - 24" X 3/8 threaded rod ($1.97)
2 - Packages - Crown Bolt Black 7/16 in. Neoprene Washers (3 Pieces) Part #030699892181 (.81 ea)
4- 3/8" hex nuts Part # 0000-655-449 (.12 ea)
2 - 1/2" hex nuts Part #oooo-655-465 (.20 ea)
6 - 5/16" cut washers Part# ABB (.12 ea)
Just over $7.00.....
Started by assembling one end
Neoprene washer - Cut washer - 3/8 nuts - Cut washer - Neoprene washer - 1/2 nuts - Cut washer - 3/8 nuts
The final 3/8 nut should be at an end of the threaded rod.
Repeat the process above on the other side.
Tighten, you will need to adjust the washers with the 1/2 nut as there is some up/down play on the threaded rod. The washer needs to align with the nut to allow the spike to slide over.
Cut the excess threaded rod at the end of the outer 3/8 nut.
The 2nd neoprene washer helps to ensure a snug fit of the spike on the 1/2 nut.
I have a couple of pictures(not sure how to imbed them in the post) in my profile (Did not think about a "How To" until it was all assembled.....
The same size spikes will also fit on the nuts (with a little 3M two sided tape) at the top of the fork tubes.
Thanks for looking.
****I make no claims to durability or longevity*****