[philso]

If you purchased "regular" boards and cut them to 5" wide, I would suggest replacing them with 3/4" BC sanded plywood (23/32" is equivalent). I understand that the rules allow "solid, robust wood" but our experience has been that it is hard to make good bumpers with anything other than plywood.

The regular boards have grain only in one direction. Depending on how you are constructing your bumpers, the grain only going in one direction may lead to splitting if you are driving screws into the wood near the ends. Impacts may also cause the wood to split where a screw was driven in near the ends. Once the wood split, we found it very difficult to repair effectively.

I specifically recommended the BC sanded (both sides) plywood over the cheaper sheathing grades (unsanded both sides) because it seems to be made from more layers of better quality wood and tends to have fewer voids. This seems to make it much less likely to split when screws are driven in near the edges and screws seem to hold better (don't strip the hole so easily).

Lowes sells half sheets (4' x 4') of 23/32" BC plywood for just over $20. The half sheet should be more than enough to make two sets of bumpers and can fit in most mid-sized SUV's. Home Depot used to sell it too but I have not been able to find any that carry it in the last couple of weeks.