Single nuts, as defined by Steinmeyer, are one-piece nuts without any shift or offset in their I.D. ball thread. They can only be preloaded by ball oversize and will always have 4-point contact. This differentiates them from all other preloaded nuts and their 4 point contact has an impact on technical data and some calculations.
The two-piece double nut from Steinmeyer has the patented UNILOCK coupling, which avoids any spacers, pins or setscrews to connect the two nut halves. UNILOCK provides an oil tight connection and resists both moments and side forces. The UNILOCK double nut is nearly as compact and stiff as a single-piece design.
Lead-offset nuts are single piece nuts with a slight shift of the thread lead approximately in the middle of the nut. This establishes a 2-point contact similar to that in a double nut, which obtains this shift by rotating the two nut halves relative to one another.
The same principle is used in the so-called pitch shift nut, but instead of a discontinuity in the lead, the pitch shift nut uses a dual start thread design with a shift between the two starts. This enables 2-point contact of the balls. Each thread start has its own set of balls and ball returns.
Exclusively for our miniature ball screws, Steinmeyer offers this unique design. Two nuts in a housing are separated by a spring. The spring action applies constant preload and eliminates play regardless of wear or manufacturing tolerances.
Steinmeyer labels all ball nuts that have 2-point ball contact a "double nut", regardless whether the nut body is made of two pieces or one. This definition makes sense because both of these nuts have very similar properties, and because all life calculations for these nuts are done in the same way. 4-point contact ball nuts on the other hand require different calculations, specifically how preload is handled in the life calculations.
Steinmeyer's patented UNILOCK coupling of two-piece double nuts results in a connection that is nearly as stiff and compact as a single-piece nut. This is why we do not distinguish between single-piece double nut design (the lead-offset nut) and a two-piece design (UNILOCK double nut) in this catalog. Steinmeyer will select whatever design is most suitable for the particular size of ball nut.
All nuts with 2-point contact can be recognized by the "5" in the 2nd number of their series designation (for example 1516, 3526 etc.).