our company keep this hole for two reason :
1) whey the wokers weld the beam ,some welding slag will come into the box beam ,so the wokers can pour-out the welding slag through the hole .
2) when our company powder coating the beam ,we will use water to clean the surface of beam ,so some water will come into the beam ,if we keep this hole ,the water will flow out through this hole .
if the customer do not want this hole ,our company can raise the box beam ,then there is no holes .
the sample that i send you ,i think the distance between the beam and the top of the connector is 40mm ,we can raise the beam ,and change the distance to 5mm ,then there is no holes .