A 'wear and tear' item simply means that it is an item which might be expected to need replacing or repairing earlier than the larger unit into which it is fitted.
For instance, vehicle cam belts, clutches, computer hard drives, which fail earlier than the expected life of the car or computer, might be claimed to be 'wear and tear' items and therefore not replaceable as part of a guarantee.
Even though those items might expressly be excluded by a manufacturers or retailers warranty, they are still subject to the statutory requirement that they keep on working for a reasonable period of time – that they are of satisfactory quality.
If the clutch on your car fails after only 30,000 or 40,000 miles, or if the cam belt fails earlier than its expected life, or if a hard drive fails earlier than the manufacturers claims for it, then it has not given satisfactory service for a reasonable period of time.
Don't give in to 'wear and tear'. 'Wear and tear' is a throwaway line which is used to distract you and divert you away from your statutory entitlements as a Consumer