A thicker butyl correct tube made for the 185R15 and 185/70R15 tyres, and nothing else.

These are a top quality correctly sized tube, with the tyre size it fits written on the side. Not some code which you later find is recommended for many tyre sizes. This is why Blockley has had to produce its own inner tubes, rather than source them from elsewhere. Tubes are the one thing you really should not be skimping on. There will be tubes that cost more than a Blockley, but we can assure you they did not cost more to make! And all Blockley tubes come as standard fitted with a metal dust cap, which the "expensive" brands charge extra for.