Good quality 20/21" Blockley Rim Band suitable for 20" and 21" wheel sizes.  At 40mm wide these bands are the best width to use for the narrower rim widths. The purpose of the rim band is to protect the inner tube from the spoke heads that are in the well of the wheel. Any other spokes are covered by the bead of the tyre.

Rim bands are often an overlooked item where people often use tape or similar wound around the wheel well, which with time goes hard and cuts the tube around the spoke heads where the heat affects it. An inexpensive Blockley rim band (£3 each) is a much better solution - and we sell our products for less than the alternative brands that cover the range 18, 19, 20 and 21" wheels! We see other rim bands made from harder material, with little elasticity and feathered edges that go hard and again cut tubes and operators fingers when they come to remove them. In short this is why Blockley makes rim bands, so we have products as they should be.
The Blockley rim bands are made from a softer compound with square cut edges which work the best. This level of attention to detail (as with all our products) really is important. Rim bands are only necessary in the wheel well of wire wheels, where exposed spoke heads are present. Insulation tape is not adequate, and the area over the spoke heads get hard with the heat and eventually cut the tube.