If you are talking for AI-P lenses, then there is absolutely no risk (see the other's answers giving the compatibility link).

But it looks you are talking more of a pre-AI lens (original F lenses) where the P was meaning "Penta" for 5 elements. In that case there are two answers:

1. The lens is original: it can cause a problem with cameras who have the small AI indexing ring around the mount (For example: D300, D500, F5, F6) but it looks the entry level digital cameras like series D3xxx and D5xxx does not have such AI indexing ring, then it would mount without issues, except there will be no metering. There is one Exception in the digital world: The Nikon Df can also accept pre-AI lenses by changing the meter coupling level as in the old Nikon F4.

2. The lens is a modified AI, then it must be considered like an AI lens in the compatibility charts.

For better seeing what I am talking about, here are some links:

• Mir.com.my, a very well documented Nikon history site
• Article about AI/AI-S and non-AI lenses from Nikon Support
• Ken Rockwell site (already mentioned)

AI Conversion links:

• KenRockwell AI'd
• Homemade conversion
• AI Kits

Apart of this and just a historic reminder, the Nikon F4 (analog) have the AI indexing switchable in order to mount such old lenses. I also own a bellows PB-4 which is supposed to be in pre-AI but as there's no aperture ring, I can mount it on my D300 without issues even the camera have the AI indexing ring (which is not compatible with the pre-AI lenses).

The potentially breaking thing, is the aperture ring of the pre-AI which is not the same shape as the AI mount and could not be mounted.

When you try to mount the lens, you can see if it goes smoothly or not, in the later case, do not force to mount it.