Pipe sizes

ive got a large car heatercore with and ID of 15mm on the barbs and roughly 16mm OD, my WB has a ID of 10mm and od of 12mm

i will be aiming to get some more 1/2 inch barbs on pump and other WB.

what size pipe should i be looking for? will i need an adapter for the heatercore?(it has large barbs 4.5cm long)

Also iam looking at a Manifold with multipul in's and outs

(1 IN 3 out - varable barb size & and on the other half 3 IN 1 out with varable barb sizes pic here http://www.overclockedpc.co.uk/images/disti_lrg.jpg)