Ford Rangers to 2006, I am not sure about the TDCi engines from 2006, although the brakes may well be the same, had TOKICO front calipers with 42mm pistons on the twin piston version. Some of the earlier versions had single piston calipers.
If you have a seized piston, you can buy from Brake Part Superstore,
or Brakes International
and maybe other places, a caliper service kit at a cost of about £18, that provides two fluid seals, two dust seals, two rubber boots for the slide pins and two bleed nipple caps.
These are a Budweg product and that company is based in Denmark.
Here is a link to the website
You can also buy a NEW Budweg piston at a cost of about £16.
I have some experience of repairing calipers and having tried, just recently on my Ford Ranger, which had a seized piston on the front left hand caliper, to replace the seals and piston at a cost of some £48 with VAT and postage, my advise is DO NOT bother trying.
The replacement caliper from the above companies, a Budweg refurbished TOKICO caliper is £80 PLUS VAT, and a surcharge of £20 until the old caliper is returned
I have NOW found a far cheaper option from this company - (note I have no connection with them - I simply bought from them)
where a refurbished TOKICO caliper, refurbished by Brake Engineering of Birmingham (UK) will cost you
£55.21 plus VAT and £6.95 postage plus VAT, with a £25 surcharge, refundable when old caliper is returned.
Service and speed of delivery was excellent.
NB - common cause of course of seized pistons is a failure to change the brake fluid, at least every two years.
Hope the information helps.
It is simply not worthwhile attemptiing repair.