Hey Bill, Merry Christmas to you and yours from Nella and I!!
Now, on to the question... If it is a damageable part I will just include insurance for the full sale value of the item being shipped. Also, it depends on the shipping company being used. All of the big shippers have some level of insurance built in to their standard quote, provided that the item is packaged in accordance with their coverage. UPS covers items up to $100.00, then additional insurance is required if the value exceeds that. I'm not sure what the insurance actually covers short of the package being outright destroyed by THEIR sorting machines. Broken items not packaged sufficiently will never be covered, and of course when dealing with any insurance related business, just expect a NO answer!!!
Now, if the item is not easily damaged, I will offer insurance as an option, but one thing I ALWAYS include is delivery confirmation. I use this as a way to confirm with the purchaser that their item has actually been shipped, and also in the (hopefully) unlikely event that the item doesn't arrive, or has arrived and the buyer is somehow being dishonest.
I have shipped hundreds of items, and can count on one hand the number of times that an item has not arrived safely. Even overseas items have somehow eluded the nightmares that can befall a shipped item. In the end, you just gotta pack it like it's going to the King, and hope for the best!!! Good luck, Geof