Andrew,

That is the exact same hot air welding tool we got.

To weld our 5,6 and 10mm HDPE we use this nozzle for it:

http://www.leister.com/en/plastic-welding-product.html?catalog=1b301b71-fc43-4641-8ef0-506387c3ebfd&subcatalog=&product=d721ddda-550f-4da4-8508-a7da56a2311b&view=sparepart&sparepart=78f6c3af-f5e9-49ab-8731-cacab916cb0ehttp://www.leister.com/en/plastic-we...01b71-fc43-464 1-8ef0-506387c3ebfd&subcatalog=&product=d721ddda-550f-4da4-8508-a7da56a2311b&vie w=sparepart&sparepart=78f6c3af-f5e9-49ab-8731-cacab916cb0e

Works like a charm.