Use a mullion op (Rule Type 142 Add Op Mullion): it finds where a mullion or meeting rail
runs into the frame and puts the notch on the frame bar, centred on the mullion (or offset from its centre line).
The op is written at the mullion’s level (Mullion or Meeting Rail) and sent to the frame with Set Op on Level=?.
How op rules work in general: How machining rules work.

Example A: frame head notch for a vertical mullion (series 6000)

Sub-routine series 90 “6000 Mullion”, rules 371–382, called from series 220 “6000”
rule 801 (a Rule Segment at level Mullion). All rules: Level Mullion, Position Vertical,
Condition L/T Out (the top end of the mullion runs out to the frame), no test.

In plain English: To notch the head of a 6000 frame where a vertical mullion’s top end lands on it, the rule
runs pattern 61TH on the frame’s top bar (6000F profiles only), at the centre line of the
mullion, when the mullion’s top end runs out to the frame.

The same sub-routine has three sister blocks: rules 383–390 for the sill (Condition R/B Out, side
2), 392–398 for a horizontal mullion into the left jamb (Position Horizontal, Condition
L/T Out, side 3) and 400–404 for the right jamb (R/B Out, side
4).

Example B: jamb notch for a meeting rail (series 6000 MR Ops)

Sub-routine series 343 “6000 MR Ops”, rules 199–219, called from series 220 “6000”
rule 859 (level Meeting Rail, Position V & H). Rules 199–211: Level Meeting Rail, Position
Horizontal, Condition L/T Out (the left end of the rail runs out to the frame).

In plain English: To notch the jamb where a horizontal meeting rail meets the frame, the rule runs pattern
61TI on the frame’s left jamb (6000F profiles only), at the centre line of the meeting
rail, when the rail’s left end runs out to the frame. Rules 213–219 repeat it for the right jamb
(Condition R/B Out, side 4); rules 228–242 do a vertical meeting rail into the head
and sill (Position Vertical, sides 1 / 2).

Holes beside the rail. The same sub-routine drills hardware holes at fixed offsets from the rail: rules
307–332 “TOC Operation 1/2/3” are three 142 blocks with pattern TOC on the frame’s left
jamb, offsets -0.25, 2.21875 and 3.28125 inches from the rail centre line. To
drill a hole a fixed distance from a mullion or rail, copy the notch block and change only the pattern and the
offset.

Build your own

1. Write the block at the level of the bar that crosses (Mullion or Meeting Rail), Position Vertical or
   Horizontal to match it.
2. Pick the Condition for the end you care about: L/T Out = top (vertical) or left (horizontal) end meets
   the frame; R/B Out = bottom or right end. L/T In / R/B In = that end stops on another mullion
   or rail instead.
3. Set Op on Level=? = 1 (frame) and Set Op if Side? = the frame bar the end lands on:
   top end → 1, bottom → 2, left → 3, right →
   4. One block per end.
4. Set the frame’s Reference, the pattern and the offset (0 for centred).