As the locking mechanism of my Ikea Tärnö table broke (soft metal + thread = bad), I designed a replacement part. It's working with an hex M6 bolt (lengths of 15mm to 20mm will work) and a wing nut. The screws of the existing mechanism are reused.

I'd suggest printing with UV-resistant materials like ASA or PETG with 100% infill and supports on build plate only. Also keep in mind to use stainless steel bolts and nuts when used outdoor.