Horizontal flow of discrete objects through a bottleneck is prevalent and important in nature and industry. In this paper, we experimentally investigate the frictional effect of the bottom wall on the flow rate of granular part ides passing through an aperture on a conveyor belt, since the bottom wall is always assumed to be trivial and the issue remains elusive. The flow rate monotonically increases with the coefficient of friction, finally approaching a saturation plateau. The bottom wall has an obvious effect on the flow rate. We show that the lateral motion of particles on both sides of the aperture, which is influenced by the coefficient of friction and can be converted into an effective aperture width, is responsible for the variation of the longitudinal flow rate. Our findings may provide a new way to manipulate the horizontal flow rate, particularly for the case where the aperture has to be fixed. (C) 2020 Published by Elsevier B.V.