A screw that belongs to the shed, not to the tyre. I called the company where I purchased the tyres and asked for a home visit. The person was not very happy because of the distance but he promised to call back. While waiting I thought I will give it a try so I started to get the tools and loosened the screws. I placed the jack, lifted the car and got the spare tire. Okay I had some difficulties (sweating and swearing all the time) but I orientated myself to the manual and --- two hours later the spare tire was on. My very first tyre change successfully done. And - because I also included an insurance with my last purchase I didn't pay a cent for the repair.