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                Safety Eligibility Letter SS-38
  
  **Hardware Type:**
            Sign Supports, Mailboxes, and Delineator Posts
                          **Code:**
            SS-38
                          **Date:**
            10/27/1993
                                  **Manufacturer:**
            Unistrut Corp.
                          **Device Description:**
            Telespar Cast Iron Three-Bolt Slip Base
                          **View PDF:**
            ss38.pdf (357.63 KB)
    
    
United States Department of Transportation - Federal Highway AdministrationOctober 27, 1993
  Refer to: HNG-14/SS-38
  Mr. Herbert J. Henry
    Telespar Product Manager
    Unistrut Corporation
    35660 Clinton Street
  Dear Mr. Henry:
  Thank you for your September 23 letter to Mr. James H. Hatton, Jr., requesting 
    acceptance of a revised Telespar post and slip-base assembly as meeting Federal 
    Highway Administration's breakaway requirements.  Our acceptance of the original 
    three-bolt, slip-base design was dated May 1, 1991.  The revised design shown 
    on the enclosed drawings, uses heavier gauge base and sign posts as well as 
    a heavy-duty cast iron slip-base assembly.
  Specifically, the hardware consists of a TL-200-B5B5 slip-base assembly with 
    76-mm x 76-mm x 4.76-mm ( 3-inch x 3-inch x 3/16-inch) structural tubing for 
    both base post and sign post.  The TL-200-B5B5 is composed of two cast iron 
    TL-199-B-5 sub-assemblies, a Teflon keeper plate between the sub-assemblies, 
    two stainless steel bushings around each attachment bolt, (one above and one 
    below the keeper plate), and two plate washers, (one under the head and one 
    under the nut of each of the three attached bolts).  The surfaces in contact 
    with the Teflon keeper plate are milled flat.  The TL-199-B5 has thicker slip 
    plates than your company's previous sum-assemblies [19-mm versus 13-mm (3/4-inch 
    versus 1⁄2-inch)].
  We note that the mass of the components in the new design is greater than 
    that of the previously accepted design.  However, it does not begin to approach 
    that of the typical large ground-mounted sign supports that commonly use slip-base 
    breakaway technology.  Since the accepted design resulted in low test occupant 
    impact velocities, we conclude that the moderate increase in post mass would 
    not results in the new design causing unacceptable occupant impact velocities 
    if it were to be tested.  Therefore, based on the successful testing of the 
    lighter gauge breakaway three-bolt slip-bases and the similarities between 
    the cast design and the accepted fabricated design, we find the new design 
    acceptable for use on the National Highway System (NHS) if requested by a 
    State.
  A caution is appropriate for all of your company's cast iron slip-base assemblies.  
    While you state that the slip plane surfaces will be milled smooth, and the 
    drawings show that the galvanizing is to be wiped smooth of these surfaces, 
    no mention is made of the opposite surfaces ob the sub-assemblies.  Since 
    the clamping forces of the bolts and washers act on these surfaces, they too, 
    must be smooth enough to permit the washers to slide.  We assume that your 
    company's quality control is sufficient to assure that there are no irregularities 
    between these surfaces and the washers that would increase friction over your 
    earlier designs.
  All other conditions in our earlier letter on the Unistrut three-bolt slip-base 
    are applicable.
  Sincerely yours,
  Lawrence A. Staron, Chief
                                                                                        
    Federal-Aid and Design Division
  3 Enclosures (Drawing Sheets)
  Geometric and Roadside Design Acceptance Letter SS-38
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