Hi SB
Apologies for this. You are correct that it should be clamps 2-5 for an Xtreme25 pole.
There were a few sent out like this by a member of staff who did not know that all clamp kits started from No.2. In each case the client was rung and either spoken to or a message left on their answer phone and the extra size clamp sent out separately.
It may be that you have a phone message you have not heard yet and the clamp is already on its way to you. I will get the staff to check tomorrow morning and if your clamp order slipped through the net they will then send out a No.5 clamp for you.