Hi,
Any picture ?
Be shure you own the proper tube diameter.
Even if inside diameter is 2mm, there's some 3 and 4 outside diameter.
If there's just a small difference that prevents you to insert the part,
you can heat the flange into boiling water
and cool down the insert into the freeser before instert it.
Metal shape can change when overheated.
Consider some parts are consumables,
and keep some stock of indispensable parts, like nozzle, heatbreaks...
++JM