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They are through screwed to the back post with machine screws.  The hole in the back post will be plugged.

Over the decades I've put plenty of furniture and other wood structure together with? machine bolts, This is what I've learned:

?In one short sentence:?? Machine bolts are unreliable in wood when installed to be inaccessible later on.

Wood moves.? That's the greatest?? issue in steel hardware.? Normally? to get a? machine bolt? to perform properly? one has to torque it to some known spec. This stretches the bolt to a known amount? falling within the? recovery curve of? the youngs modulus for the bolt material.? The fact of the bolt stretching? obviates? the need of use of a lock washer.

That is to say the bolt is deformed by stretching but when? loosened? will recover it's dimensions? with out issue because? the stretching? is inside the point? of deformation at which the material would be permanently? deformed. .? There is a different? youngs modulus of elasticity? for every? alloy and every? material.?? IT is why? German engineers do not specify? lock washers on their? fasteners.? They specify a torque.

Cheap shit? A36 alloy Steel Bolts sold to the retail consumer? are? often an exception because? little attention is paid to the alloy often called Chinesium.? China makes a great? amount of steel from the? hammered off black scale?? ( that black shit on hot rolled steel that you gotta remove to TIG it or Paint it). Theoretically? the?? scale is the exact same alloy as the underlying steel but? they get it from everywhere so? the term "alloy" is? unhelpful.? It is usually OK steel for run-of-the-mill work? but? is is unreliable for closely? specified work.

Anyway all that said,? the bolt? even when tightened to the proper torque? to stretch it that little bit necessary to? eliminate any need for lock washers? is still an issue in wood because wood moves.? It moves in response to humidity and it? creeps under pressure.

I've used oversize washers and backing plates and if they are big enough? it lets me maintain that torque setting ? for a very long time in very hard lumber.? But it still moves.? I have tried Spring Washers ( marvelous little things)? and? that? does? work better. But there's no perfect cure all pill.

Revisiting my work? years? even decades later I have? observes that bolts I thought I had torqued properly? were? often? loose and rattling around.?? Not always,? but often enough to discourage me from? covering them with? plugs and making them inaccessible.

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