Wich Game???? What year???? Different stops for different designs...

Try pbresource:
AC/DC coil stop all in one
WLL-A8143+ $4.50ea
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Coil stop is designed to replaces
Williams A-7414 AC coil stops.
http://www.pbresource.com/KT-WFLIP03.html

Rebuild kit for 1975 Williams flipper
http://www.pbresource.com/rebuildk/kt-wflip-04m.jpg

O.K. That is a picture using pbresource parts...
1) what does your coil stop look like? ....
-- A-7414 OEM from Williams does not exist anymore...
2) pbresource redesigned an A-7414 like coil stop for AC voltage designed pinballs.
3) marcos specialties A-7414 coil stop references A-8143 coil stop...
4) A-8143 coil stop is a DC voltage coil stop, it is not a AC voltage coil stop.

1) OEM = Original Equipment Manufacture
2) "The one from pbresource also refers to A8143"
2) Answer: Yes! notice the "+" symbol after the part number from pbresource
--- the part they make is a hybrid part. Like I noted above it is a AC/DC coil stop.
3-4) "I would expect the coilstops to fit AC coils."
Answer: Yes, the part Marcos sells does fit the original bracket.
-------- But, Marco is more into solid state games rather than the old
-------- electro-mechanical games.
Note: Marco is also making their own parts to replace NLA parts...
------ It does not mean they are making the part correctly for the style of game one has.

coilstop (resized).png

Answer: AC coil stops need a copper core to breakup the AC frequency, AKA Hertz, current cycle.
------- The brass collar is used to demagnetize to two pieces of metal....
------- [a. the plug][b.the mounting bracket]
------- The coil stop has to collapse the magnetic field that surrounds the coil when deactivated.
Note: you will find stories in Pinside of coil stops being magnetized from time to time.
williams coil stops (resized).jpg
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Here you can see the copper core.
Also, the brass collar.
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