We bought our square ring insert at Lowes.

I actually will use the metal fire pit that I have now to lay inside the structure that you see in the pictures.. That way I can clean it out really easy.

Now THIS suggestion is the BEST. Just be sure you do use wood and not charcoal briquettes if you are adding ashes to compost/garden.

Isn’t a semi rim round? If so, how will that work for a square fire pit?

I built mine the same way except I used the bottom of an old kettle bbq instead of the fire ring. It makes cleaning so much easier – just lift the bbq out of the rocks, being careful not to dislodge any of the stones so it’ll fit back in place. Then I dump the ashes in my compost pile or around my garden. You can rinse the bbq out with the garden hose if you want. Then set the cleaned bbq back in it’s hole – it’s all clean & ready for your next firepit party.

What works for me is to use a small/hand gardening rake to get any pieces bigger than an inch or so then vacuum out the rest with a shop vac. If you have really small rocks or sand in the bottom, the vac might suck them up also.

Of course, wait until it has completely cooled off. (I usually just do it before the next use)