This rarely happens, however some lumber seems to be just slightly thicker than others. Although it is close to 1-1/2" thick, it can be just slightly thicker. Sometimes the lock washers can be a little thicker, or the bolts can be a little shorter. In all these cases, we've found a few things that seem to help:
- Clamping the wood together will sometimes bring it close enough to get all the hardware on the bolt and the nut started.
- Since most of the bolts are in sets of two, you can assemble one bolt without one washer and tighten it to get the washers and nut started on the other one. Then unscrew the first one and add the washer you removed and re-tighten it.
- You may be able to start it without the lock-washer and tighten it enough to make a slight indentation in the wood. Then remove the bolt and add the lockwasher back.