My 185 came with the cold weather plates, but not the screws to hold them on. Here’s a photo of the rivnuts they screw into. Any idea what screws I’d need?

Measure the screw diameter to determine the screw diameter. Measure the necessary length by measuring the thickness of the plate plus the washer and lock washer you will need under the head of the screw. Make sure you have plenty of thread engagement.

Given these may well be aluminum rivnuts intended for reasonably short-term installation (i.e. they are not buried under 10 feet of impenetrable structure, never to be seen again once installed) I would suggest you likely will appreciate the appearance of a stainless steel (CRES) screw and mating flat washers and lock washers.

With this in mind I would suggest you contemplate something like the following:
Screws - AN526C-832R8 or R10 (R designates length in 1/16" increments) (I'm assuming these will prove to be 8-32 fasteners but may be 10-32 - if so, change the part number to AN526C-1032R8 or R10)

Washers - AN960C8 (I'm assuming these will prove to be 8-32 fasteners)

Lock washers - MS35338-137 for 8-32 fasteners or -138 for 10-32 fasteners

Hope this helps.

Have same on our early 210. Pretty sure they are 10-32. Very helpful on cold days for both engine and pax comfort. Only below 20F in 210’s case.

Thanks, Av and Mark.

It is shown in the 180/185 IPC

Interestingly, the IPC calls out "AN525-823R8," which Google says doesn't exist. I assume it's a typo and it's meant to be -832R8. For 17¢ each, it's a chance I'm willing to take.

be careful about using stainless screws in an Aluminum nut. any corrosion an they will lock and you will twist the screw off. If the the rivnuts are aluminum use conventional steel screws.

Interestingly, the IPC calls out "AN525-823R8," which Google says doesn't exist. I assume it's a typo and it's meant to be -832R8. For 17¢ each, it's a chance I'm willing to take.

Bill - note my caveat with respect to location of these fasteners and frequency of access. Corrosion is unlikely to be a problem since the cold weather kit is typically installed for only a short portion of the flying year.

If it's of any worth, I've been using CRES fasteners in similar applications without corrosion. Living where there's snow is a lot different from living where there's lots of humidity and salt in the air!