Compression fitting with visual torque indicator

1. A tubing nut fastener comprising:

a nut having:

first channels disposed circumferentially and spaced radially along an inner surface proximate to a first end; and

an inner ring radially projecting from the inner surface and proximate to a second end;

a main body having a third end and a fourth end, and including:

a reference mark disposed on an outer surface; and

second channels disposed circumferentially and spaced radially along the outer surface proximate to the fourth end, wherein the inner surface of the nut surrounds the outer surface of the main body at the fourth end; and

engagement members disposed within the first channels and the second channels between the nut and the main body;

wherein at least one of the first channels and the second channels vary in depth along a length.

2. The tubing nut fastener of claim 1 , wherein:

the first channels vary in depth along the length.

3. The tubing nut fastener of claim 1 , wherein:

the second channels vary in depth along the length.

4. The tubing nut fastener of claim 1 , wherein:

the main body includes an inner surface having interior threads proximate to the third end, and

the first channels have centerlines with non-zero angles that are based on a thread pitch of the interior threads.

5. The tubing nut fastener of claim 1 , wherein:

the main body includes an inner surface having interior threads proximate to the third end, and

the second channels have centerlines with non-zero angles that are based on a thread pitch of the interior threads.

6. The tubing nut fastener of claim 1 , wherein:

the engagement members comprise balls, and

the nut includes ports in the inner surface that extend from the first channels to the first end, and are sized to receive the balls.

7. The tubing nut fastener of claim 1 , wherein:

a spatial relationship between the reference mark and a visual indicator on the nut indicates whether the tubing nut fastener is in a torqued state or an un-torqued state.

8. A method of fabricating a tubing nut fastener, the method comprising:

providing a nut having first channels disposed circumferentially and spaced radially along an inner surface proximate to a first end, and an inner ring radially projecting from the inner surface proximate to a second end;

providing a main body having a third end and a fourth end, and including a reference mark disposed on an outer surface, and second channels disposed circumferentially and spaced radially along the outer surface proximate to the fourth end; and

engaging the first channels with the second channels using engagement members, wherein at least one of the first channels and the second channels vary in depth along a length.

9. The method of claim 8 , wherein:

the first channels vary in depth along the length.

10. The method of claim 8 , wherein:

the second channels vary in depth along the length.

11. The method of claim 8 , wherein:

the main body includes an inner surface having interior threads proximate to the third end, and

the first channels have centerlines with non-zero angles that are based on a thread pitch of the interior threads.

12. The method of claim 8 , wherein

the main body includes an inner surface having interior threads proximate to the third end, and

the second channels have centerlines with non-zero angles that are based on a thread pitch of the interior threads.

13. The method of claim 8 , wherein:

the engagement members comprise balls,

the nut includes ports in the inner surface that extend from the first channels to the first end and are sized to receive the balls, and

engaging the first channels with the second channels comprises:

aligning the first channels with the second channels; and

loading the balls into the first channels and the second channels using the ports.

14. A method of terminating tubing at a connector using a tubing nut fastener, the method comprising:

sliding a ferrule into the tubing nut fastener, wherein the tubing nut fastener includes a nut having first channels disposed circumferentially along an inner surface, a main body having second channels disposed circumferentially along an outer surface, and engagement members disposed within the first channels and the second channels between the nut and the main body;

installing the ferrule and tubing nut fastener onto an end of the tubing;

rotating the tubing nut fastener to engage interior threads of the main body with exterior threads of the connector; and

applying a torque to rotate the nut with respect to the main body to reduce a relative depth of the first channels and the second channels across the engagement members and generate a torsional spring force which biases the nut in a direction of rotation with respect to the main body.

15. The method of claim 14 , further comprising:

determining that the tubing nut fastener is in a torqued state based on a first spatial relationship between a reference mark on the outer surface of the main body and a visual indicator on the nut.

16. The method of claim 15 , further comprising:

determining that the tubing nut fastener is in an un-torqued state based on a second spatial relationship between the reference mark and the visual indicator that is different than the first spatial relationship.

17. The method of claim 14 , wherein:

the first channels vary in depth along a length.

18. The method of claim 14 , wherein:

the second channels vary in depth along a length.

19. The method of claim 14 , wherein:

the first channels have centerlines with non-zero angles that are based on a thread pitch of the interior threads.

20. The method of claim 14 , wherein:

the second channels have centerlines with non-zero angles that are based on a thread pitch of the interior threads.