As of Monday 8th June I have decided not to use Royal Mail 2nd class any more to keep the price of a clip or washer down to something reasonable. The service has become extremely unreliable. I know from my own experience of receiving that our mail seems to be delivered weekly at times, with some mail taking 2 weeks to get to us and feedback from customers has been that many see similar 1-2 weeks for delivery.
I have tried to stick with it in recent times because I am reluctant to charge too much just for a clip, washer or bobbin.
But going forward, unless ordered with other items, the large letter items will be shipped with the Royal Mail Tracked 48 service for standard shipping (2-3 days typically) and Tracked 24 for express.
These are not guaranteed next day and 2 day, They are 1-2 days and 2-3 days typically and can be a day or two longer to the islands around the UK and customers will have the benefit of tracking to their email and/or mobile.