Lock nut for Sunday Cat tabernacle ?

[Steve Caplow]

I know his sounds like a silly request, but does anyone know the size of the locknut in the tabernacle so I can order one? As I was reinstalling the sail and replacing the bolt in the tabernacle, the nut fell and was nowhere to be found. I'm currently traveling and would like to order a replacement ( so I can't directly measure the other nut/bolt. Thanks!