The use of column-tree connections is common in controlled shop environments due to their cost-effectiveness in achieving ductile welds. Field bolts are also easy to install and inspect. However. there is currently no prequalification available for these connections. https://www.spidertattooz.com/CYMA-Sport-M4-Airsoft-AEG-with-11-UX-4-Modular-Handguard/