Anything to do with plumbing is always going to make people nervous. The first thought when considering plumbing fitting, is that plumbers are the highest paid artisans in the world. People who attempt to purchase and fit their own plumbing fittings are indeed very brave as plumbing fittings are the true watershed for deciding if a person is a true do it yourself hero or just a pretender who enjoys buying and playing with fancy tools.
Plumbing fittings even manage to look intimidating, which is hard for inanimate object, but because they are all so similar and yet so different, one has to be so careful when purchasing any plumbing fittings. The smallest mistake could end up costing you a small fortune in repairs, to not just the plumbing system but also to the rest of your home, that would have affected by the water damage.
This is why plumbers charge the absolute earth to install even the simplest of fittings. They know the risks of making a bad plumbing decision. One millimetre may not sound like much, and if you were dealing with anything other than plumbing fittings it definitely would not be, but in the world of plumbing fitting a one millimetre mistake could lead to thousands in water damage.
If you are brave enough to take the purchase of plumbing fittings to fix anything to do with the sewage system then you really are brave, or maybe stupid. This is an area of plumbing where the margin for error, which is small anyway, gets down to zero. It is never a good idea to go shopping for plumbing fittings for the sewage system unless you have the most precise measurements because the amount of money which that particular gamble will cost you will make a trip to Vegas seem like a charity holiday. So when buying plumbing fittings, and you are not a plumber, follow the idiot proof rules that were laid down by the do it yourself ancestors and measure everything at least twice and then do it again because if you do not you will regret it for a long time to come.