Armor spikes deal extra piercing damage (see “spiked armor” on Table: Weapons) on a successful grapple attack. The spikes count as a martial weapon. If you are not proficient with them, you take a –4 penalty on grapple checks when you try to use them. You can also make a regular melee attack (or off-hand attack) with the spikes, and they count as a light weapon in this case. (You can’t also make an attack with armor spikes if you have already made an attack with another off-hand weapon, and vice versa.) An enhancement bonus to a suit of armor does not improve the spikes’ effectiveness, but the spikes can be made into magic weapons in their own right.
Pathfinder Roleplaying Game: Ultimate Equipment (OGL) © 2012, Paizo Publishing, LLC; Authors: Dennis Baker, Jesse Benner, Benjamin Bruck, Ross Byers, Brian J. Cortijo, Ryan Costello, Mike Ferguson, Matt Goetz, Jim Groves, Tracy Hurley, Matt James, Jonathan H. Keith, Michael Kenway, Hal MacLean, Jason Nelson, Tork Shaw, Owen KC Stephens, Russ Taylor, and numerous RPG Superstar contributors