Ceramic Tap Problems

50Twuncle

I have a dripping kitchen tap (ceramic 1/2 turn) and need new cartridges
I don't know whether I need 8mm or 9mm
B&Q offer both
Is there some way of finding out - prior to buying ?
ie http://www.diy.com/diy/jsp/bq/nav.jsp?isSearch=true&isYmal=true&fh_search=0000003894491
or
http://www.diy.com/diy/jsp/bq/nav.jsp?action=detail&fh_secondid=11477997&fh_reftheme=promo_161448252%2cseeall%2c%2f%2fcatal!!!1%2fen_GB%2fcategories%3c%7b9372015%7d%2fcategories%3c%7b9372046%7d%2fcategories%3c%7b9882012%7d&fh_view_size=12&fh_location=%2f%2fcatal!!!1%2fen_GB%2fcategories%3c%7b9372015%7d%2fcategories%3c%7b9372046%7d%2fcategories%3c%7b9882012%7d%2fspecificationsProductType%3dtaps&fh_eds=%c3%9f&fh_refview=lister&isSearch=false#ancBVQuestionsContainer
or is 9mm ceramic and 8mm not ?

27col

Simple! You buy one of each and get a refund on the one that you don't use.

50Twuncle

Done just that - and the cost was a mere £9.99 for both taps - much cheaper than the £75+ that a plumber would charge for the job....
It was a simple, unscrew, clean out and replace job
Plus a nice feeling of satisfaction too !!!