Hangar 9 P-51D 1.50 ARF Assembly Manual page 14

Section 2: Aileron and Flap Servo Installation
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. . . .Step 10
Assemble.the.aileron.linkage.using.two.clevises,.two..
4-40.nuts.and.a.4-40.x.2".threaded.rod.
   
. . . .Step 11
Use.a.7/64".drill.bit.to.drill.out.the.mounting.holes.in..
the.control.horn.
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   
. . . .Step 12
Attach.the.clevis.to.the.control.horn.and.servo.arm..
Position.the.control.horn.on.the.aileron.by.aligning.the.
linkage.with.the.servo.arm.slot.and.aligning.the.holes.of.
the.control.horn.with.the.hinge.line.of.the.aileron..Use.a.
felt-tipped.pen.to.mark.the.locations.for.the.horn.screws.
Note:.There.is.a.hardwood.plate.
inside.the.control.surface.that.the.
control.horn.will.be.mounted.to.
   
. . . .Step 13
Drill.three.1/16".holes.at.the.locations.marked.in.the.
previous.step..The.holes.only.need.to.be.7/16".deep;.don't.
drill.through.the.top.of.the.aileron.
Hint:.Wrap.a.piece.of.tape.around.your.drill.
bit.to.drill.the.holes.the.correct.depth.