def create_expr_string(clip_level_value):
    """Create the expression arg string to run AFNI 3dcalc via Nipype.

    :type clip_level_value: int
    :param clip_level_value: The integer of the clipping threshold.
    :rtype: str
    :return The string intended for the Nipype AFNI 3dcalc "expr" arg inputs.
    """

    expr_string = "step(a-%s)" % clip_level_value

    return expr_string