Anything from small 2/4 stroke engines to big diesels.
I guess you don't miss what you never had eh! I buy tools like crows with no plan for their use. They might set in my box for a good while, perhaps even several years, then one day I will be working on something and find a tool like that will allow me to do a job in ten minutes that otherwise might have meant an hour of labor without the tool. While I am a home wrench I don't want to waste tons of time doing a job that could be done much quicker and more efficiently using a specialty tool perfect for the task.
The reason I have arrived at a lot of my ideas goes back to working on cars with my pop as a kid. My dad had one small hip top tool box with most of the basics, but almost primitive by what most here including me have in the way of tool collections. My dad did not have 1/4" & 3/8" sets, deep sockets in any drive size, specialty pliers, other than one pair of vise grips, or mega piece wrench sets. My dads open ends might have gone to 3/4" and his double box ends stopped at 15/16" or perhaps 1" no metrics, didn't need them. In fact he only later got deep sockets and the other drive sizes because I gave them to him as gifts as I got older.
My point is I recall always getting the mission accomplished when fixing a car with my dad, but I well remember the countless times deep sockets would have been a god send, or perhaps a nut buster, or crows feet or any other specialty tools almost countless in number. Yes we got the job done, but not having a lot of those specialty tools resulted in many lost hours and made the job that much more difficult. I think those memories instilled in me the idea that having a wide range of seldom used specialty tools is not a bad thing. Plus you have to remember I buy quality used cheap as I find them, or only tools on sale almost exclusively. It works for me, but to each his own.
