Subtraction from an assembly doesn't work as expected:

[gumyr]

from build123d import *
from bd_warehouse.fastener import HexHeadScrew
from ocp_vscode import show_all
import timeit


screw = HexHeadScrew("M6-1", 15 * MM, simple=False)

# Algebra
cutter = Pos(X=2 * MM) * Box(15, 15, 15, align=(Align.MIN, Align.CENTER, Align.MAX))
start_time = timeit.default_timer()
al_cut_screw = screw - cutter
print(f"Algebra Time: {timeit.default_timer() - start_time:0.3f}s")

The screw is unchanged.