Most European benches use a bolt system to fasten leg sets to stretchers. The main advantage is that you can snug the bolts if anything loosens due to changes in humidity.
The solid brass nuts on these bench bolts slide into a pre-drilled hole in the stretcher, and distribute pressure to prevent breakout. A bench can be made very rigid (without complex joinery) by using a wide stretcher, since the stretcher is bolted into position.
The steel bolts are 152mm (6in) long and 12.7mm (1/2in) in diameter. The nuts are 25mm x 25mm and will fit perfectly in a 1in (25.4mm) hole.