The connection assembly between the mask and the hose may vary depending on the mask that you have. Some of our newer masks have a white plastic coupling that fits between the mask and the hose. (right)
Some of our older masks have a reduced mask port that was designed for the breather hose to directly fit inside the hose. Here is how the old coupling assembly looks. Note the absence of the white splice piece. (below)
If you have a mask that does not require a coupling, it should slide on to the breather hose directly with little effort. If you are unable to couple the mask easily with the breather hose, then it is likely that your mask requires a coupling that should have been provided with your mask assembly.