Unlike the front struts, no new bolts are "required". However, I would recommend them, and the pic shows why... chances are your bolts are old and or rusted... be prepared before you begin your project.

You would need 4 (2 each side) PN 945444 ($2.50 ea at the dealer)...
IF you should need a nut to fit these, use PN 945408 ($1.10 ea at the dealer).

You should not need this nut unless your original setup is compromised. As for me, when my bolt head broke off, it left the bolt in the frame, I drilled into the bolt and started to use and extraction bit, but that broke, and then the bit was too hard to drill into. I had to use small bits and drill around the extraction bit, which in a couple of places transgressed the thread pattern in the frame. In the end I only had about 70% of the original threading surface, so I decided to get the extra nut, and after installing the new shock, I reinforced the underneath by adding a lock washer and the extra nut.

Note that because the nut is a "jimmy-rig" fix, it is not prescribed in the manual and no dealer will be able to find this on his diagram, so being armed with this part number will save you time and hassle going through a trial and error process.

Cheers

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1995 850T Wagon 120k

Good tip. The new bolts are low cost and would be worth replacing in any case. I tried mine (95 850 wagon 120k) this morning and they turned stiffly but not too hard. I stopped after the heads came up a bit and gave them a shot of PB Blaster. They came out fine and I reused them. This is after 10 years of MA winters.
The original Volvo bolts are strong, good quality grade 8 bolts. If they are rusted enough to break, I doubt an easy out/extraction bit will work, and you will end up as described, breaking the easy out, which is impossible to drill out. If the bolt breaks I would just drill it out and use the new bolt with a hex nut.
-Art