question of the first conv layer parameter

[kinfeparty]

model = _modify_first_conv_layer(model,3,3) ##### Check models trained (3,7,7) or (7,7,7)

I found that the the first conv layer of pretrained model of resnext101 is (7,7,7).I think because the input frame is 32.
So which input frame use the (3,7,7) conv layer?