Underlying security's SecurityType.
Valid values: see SecurityType (167) field
(see below for details concerning this fields use in conjunction with SecurityType=REPO)
The following applies when used in conjunction with SecurityType=REPO
Represents the general or specific type of security that underlies a financing agreement
Valid values for SecurityType=REPO:
If bonds of a particular issuer or country are wanted in an Order or are in the basket of an Execution and the SecurityType is not granular enough, include the UnderlyingIssuer (306), UnderlyingCountryOfIssue (592), UnderlyingProgram, UnderlyingRegType and/or UnderlyingStipulations > block e.g.: