This type couplers also called special couplers. They could be used for tube of od89mm.
KIndly attach some details for their specifications:
89mm double coupler,weight 2.59kg, 89mm swivel coupler, weight 2.71kg, 89mm half coupler, weight 2.2kg.
All this couplers are strictly controlled wtih BS1139 or EN74.
Any inspections before shipping are very appreciated at any time.