Hi @Kaneda, from the code it looks like the [3,3,3] or the [5,5,5] is an argument “num_blocks” to the function _make_layer which is being used to decide strides for different layers.

def _make_layer(self, block, planes, num_blocks, stride):
strides = [stride] + [1]*(num_blocks-1)
layers = []
for stride in strides:
layers.append(block(self.in_planes, planes, stride))
self.in_planes = planes * block.expansion
    return nn.Sequential(*layers)