VEVOR 101.6x101.6mm Post Base 20Pcs, Internal 91x91mm Heavy Duty Powder-Coated Steel Post Bracket Fit for Standard Wood Post Anchor, Decking Post Base for Deck Porch Handrail Railing Support

If these are suitable for 100mm posts then how do these work if the internal measurements of the upper opening is only 91mm. The nominal measurement of a "100mm" post is typically 97mm. Given the material is carbon steel it is unlikely that there is a 6mm give when inserting the posts? Please advise. With thanks.