Rather than change the gas pipe to the hob, why not cut off the hob fitting to suit your pipe ?
When you buy a hob, it generally comes with a formed fitting which the plumber can connect onto with standard fittings.
This pipe had been cut back and a compression fitting had been over-tightened onto it. The problem was they cut off the standard 15mm connection which meant the hob was unsafe to use.
The customer was lucky there wasn’t a gas leak and we had spotted the potential danger.
A new part wasn’t available to buy and so a new hob was bought and then fitted by us the next day.