Colin, I agree that some pattern items are the equal of the original equipment and in some cases may be identical, But, in the case of the aux drive belt on my ZX the pattern item which I fitted (a QH item I believe) the V's were narrower than the original causing it to sit further into the V's on the pully, I think the pattern belt had bottomed out and was losing drive. I used to own a 1991 BMW320, the diff output shaft seals stated to leak, I asked my local indi BMW tech if I should buy pattern replacements, he said that the originals were modded to include a double lip and that these mods hadn't filtered through to the pattern part suppliers, hence the original BMW items were a better buy. My motto now is, ask questions, read forums, then make my own mind up. It works for me, usually.