Weld pins are used for fasten the insulation to the sheet metal of air duct. We have the 1/2"-2" size same as USA standard.
China Melparts Precision Manufacturing is an ISO9001:2008 certificated  custom manufacturer which produce all kinds of metal parts for many industries, we process the CNC machining and metal stamping, the material we could process steel, stainless steel, aluminum, brass etc. we also produce the insulation fasteners for HVAC industry, we have weld pins and insulation pin, the weld pins are used for fasten the insulation to the sheet metal of air duct, the insulation pins are used to fasten the insulation sheet to the wall, weld pins' size is 1/2" 3/4" 1" 11/8" 11/2" 2" we have cup head and flat head style. more details please see: melparts.com