pipe flarer

do i need a metric or imperial, if i measure the pipe i have it doesn't measure round and about 4 - 5 mm, been looking at this flarer am i on the right track looks half decent but will it do double and single flares this type ?
http://cgi.ebay.com/RIDGID-PIPE-FLARING ... otohosting
thanks
http://cgi.ebay.com/RIDGID-PIPE-FLARING ... otohosting
thanks