Finally, both Calmark and Birtcher products have optional features to consider when choosing a Wedge Lok. These optional features may include the addition of a lock and flat washer for added resistance to loosening from shock and vibration, which is denoted as “LF” for Birtcher products or a “W” for Calmark products. Alternatively, Lock tight, which is denoted with an “L” suffix, is only available on Calmark products and can be applied to the thread of the screw. Similar to the LF or W option, this will provide further resistance to loosening from shock and vibration. There are several options to reduce the possibility of unintentional disassembly of the screw from rear wedge. The addition of a lock nut is detail “R” for Calmark or “LN” for Birtcher, or if stainless steel is preferred, a “CR” is available with some models. Another option is Calmark “K” suffix which features a slotted screw and slotted shaft, also to prevent unintentional disassembly. A visual indicator of when the unit is locked is denoted as a “V” for Calmark or “VI” for Birtcher prefix. When the wedge is unlocked, a red indicator is visible at the end of the assembly. All standard products can be directly configured using the nVent Calmark/Birtcher Specifiers guide. Any modification not listed in the Specifiers guide would classify the product as a custom, and would receive a special part number. Common modifications include a greater number of wedge segments, lengths outside of the catalog offering, relocation of mounting holes, substituting Belleville washers for split washers, different materials, or different finishes.