Yukon Grizzly locker, Ford 8.8" front with 31 splines. 
YGLF8.8-31

The Yukon Grizzly Locker is the ultimate in mechanical locking differentials for street, off-road, and drag racing. Grizzly Lockers provide 100% power to both tires, while still allowing for disengagement while negotiating turns.

Ford 8.8" Reverse Front 31 spline 

2011 and Newer 8.8 Front

• Patented internal design reduces common locker failures
  
• 8620 internals for added strength
  
• Assembled in the USA
  
• Ring Gear Diameter:  8.800
  
• Cover Bolts:  10
  
• Ring Gear Bolts:  10
  
• Spline Count:  31
  
• Carrier Breaks:  none
  
• Pinion Nut Size:  1-1/16
  

Compatible with Models:

F-150 1/2 Ton:  2009 - 2018  (Front)

F-150 Raptor Edition:  2010 - 2015  (Front)