The disclosure relates to a fastener assembly comprising a nut and a washer that insures a minimum preload on the nut and bolt assembly by load indicator means which also maintain the nut and washer in a joint preassembly.

BACKGROUND OF THE INVENTION 
Nuts having an internal thread with a wedge ramp at the root thereof, of 
the type disclosed in U.S. Pat. No. 4,076,064, are often used in 
combination with standard bolts to enhance the ability of the nut and bolt 
assembly to maintain its integrity in vibratory environments. However, the 
nature of the wedge ramp is such that reduction of axial load on the nut 
and bolt assembly below a predetermined level, caused by, for example, 
thermal expansion and lengthening of the bolt, may induce loosening. This 
problem may be solved by insuring that a minimum axial load or "preload" 
is maintained on the nut and bolt assembly. 
SUMMARY OF THE INVENTION 
To solve the aforesaid problem, a preload washer is attached to the base of 
a hexagonal nut to maintain a predetermined minimum axial load on the nut 
and bolt asssembly. The minimum load is achieved by the bias resulting 
from deflection of a convexly curved portion of the preload washer upon 
initial torquing of the nut. The convex portion of the preload washer is 
deflected until the washer is flattened against a bearing surface. Visual 
indication of condition is given by the orientation of a plurality of 
slots on the washer. 
Additional torque is applied to the nut of the assembly after a minimum 
preload is attained by the washer as required. The washer insures that a 
minimum axial load is maintained at all times on the nut and bolt assembly 
despite temperature variations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
A nut and preload washer assembly 6, in accordance with a constructed 
embodiment of the instant invention, comprises a plated corrosion 
resistant nut 8 and a dished preload washer 10. The nut 8 has a flat top 
surface 12, a flat bottom surface 14, and an aperture with a "wedge ramp" 
internal thread form 17 extending therethrough. The nut 8 has a hexagonal 
wrenching surface 16 to facilitate torquing thereof relative to a bolt 20. 
In accordance with one feature of the present invention, the nut 8 has a 
truncated conical section 22 at its base for the retention of the unloaded 
washer 10. The washer 10 has a central aperture 24 slightly larger than 
the major diameter of the thread 17 of the nut 8 to facilitate acceptance 
of the bolt 20 therethrough. 
The washer 10 has a normally convex bottom surface 26 which, upon 
flattening thereof, effects an upward bias on the nut 8. 
The washer 10 has slots 30 in an upstanding flange 32 to accommodate 
deflection thereof to the conical configuration of the base section 22 of 
the nut 8. Opposed walls of the slots 30 are convergent to each other when 
the tension washer 10 is unstressed but move into parallel relationship 
when the nut 8 is fully advanced onto the bolt 20, giving visual 
indication that the assembly 6 is fully loaded as seen in FIG. 3. 
As torque is applied to the hexagonal wrenching surface 16 of the nut 8, 
the bolt advances through the nut 8. Advancement of the bolt 20 through 
the nut 8 brings the convex surface 26 of the washer 10 into contact with 
a workpiece 40, whereupon the convex surface 26 of the washer 10 is 
flattened. The resultant spring bias on the nut 8 tends to maintain the 
bolt 20 in tension. Continued torquing of the nut 8 brings the nut 8 to a 
designated assembly load. 
In accordance with the invention, the slots 30 are orientated in parallel 
relation when the convex surface 26 of the washer 10 is flexed into a 
plane. 
Further torque applied to the hexagonal wrenching surface 16 of the nut 8 
brings the assembly 6 to full joint load requirements. 
As best seen in FIG. 4, an upward bias on the nut 8 relative to a 
complementary bolt 20 due to compression of the washer 10 maintains the 
ramp on the internal thread form 17 of the nut 8 in engagement with the 
crest of the thread on the bolt 20. Such engagement insures that a minimum 
level of prevailing torque exists between the nut 8 and bolt 20 to 
preclude spurious disassembly. 
While the preferred embodiment of the invention has been disclosed, it 
should be appreciated that the invention is susceptible of modification 
without departing from the scope of the following claims.