diff --git a/printer_mods/README.md b/printer_mods/README.md
index d1977dade..1262a03d3 100644
--- a/printer_mods/README.md
+++ b/printer_mods/README.md
@@ -69,6 +69,7 @@ like so:
 ||[Ender 3 Switchwire Y Tensioner Mod](./buzzdalf/ytension) | Y Tension Mod | :x: | :x: | :x: | :heavy_check_mark: |
  ByteChild | [ESP32 DIN Rail Bracket](./ByteChild/ESP32_DIN_Rail_Bracket) | DIN rail mounting bracket for an ESP32 | :x: | :grey_question: | :heavy_check_mark: | :x: |
  || [2-Channel Relay DIN Rail Bracket](./ByteChild/2_Channel_Relay_DIN_Rail_Bracket) | DIN Rail mounting bracket for an 2-Channel-Relay | :x: | :grey_question: | :heavy_check_mark: | :x: |
+|bythorsthunder|[MGN9 Backers Idlers](./bythorsthunder/MGN9_Backers)|New idler uppers for MGN9 Extrusion backers |:x:|:x:|:heavy_check_mark:|:x:|:x:|
 | Ch4rlesB | [V0 Handles Slim](./Ch4rlesB/V0_Handles_Slim) | Simple and slim handles for the V0 | :heavy_check_mark: | :x: | :x: | :x: |
 | chrisrgonzales | [270° Front Panel Hinge](./chrisrgonzales/270_degree_hinge) | Hinges that have 270° of swivel, parametric CAD included | :x: | :x: | :heavy_check_mark: | :x: |
 | christophmueller | [Phaetus and Zodiac Dragonfly BMO Afterburner toolheads](./christophmueller/Phaetus_Dragonfly_BMO_Afterburner) | Covers both the original Phaetus variant as well as the Zodiac one. | :x: | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
diff --git a/printer_mods/bythorsthunder/MGN9_Backers/CAD/Belt_Clamp.f3d b/printer_mods/bythorsthunder/MGN9_Backers/CAD/Belt_Clamp.f3d
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diff --git a/printer_mods/bythorsthunder/MGN9_Backers/CAD/Front_Idler_A_Top_Modified.f3d b/printer_mods/bythorsthunder/MGN9_Backers/CAD/Front_Idler_A_Top_Modified.f3d
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diff --git a/printer_mods/bythorsthunder/MGN9_Backers/CAD/Front_Idler_B_Top_Modified.f3d b/printer_mods/bythorsthunder/MGN9_Backers/CAD/Front_Idler_B_Top_Modified.f3d
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diff --git a/printer_mods/bythorsthunder/MGN9_Backers/IMAGES/Front_Idler_MGN9_Backer.JPG b/printer_mods/bythorsthunder/MGN9_Backers/IMAGES/Front_Idler_MGN9_Backer.JPG
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diff --git a/printer_mods/bythorsthunder/MGN9_Backers/IMAGES/Rail_with_idler.jpg b/printer_mods/bythorsthunder/MGN9_Backers/IMAGES/Rail_with_idler.jpg
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diff --git a/printer_mods/bythorsthunder/MGN9_Backers/IMAGES/Rails_installed.JPG b/printer_mods/bythorsthunder/MGN9_Backers/IMAGES/Rails_installed.JPG
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diff --git a/printer_mods/bythorsthunder/MGN9_Backers/README.md b/printer_mods/bythorsthunder/MGN9_Backers/README.md
new file mode 100644
index 000000000..d2f8175f2
--- /dev/null
+++ b/printer_mods/bythorsthunder/MGN9_Backers/README.md
@@ -0,0 +1,13 @@
+# MGN9 Extrusion Backer Mod
+
+A mod to allow the installation of full length MGN9 rails on top of Y extrusions to combat thermal expansion on a V2.4.  This is based on the discovery of bimetallic flexing caused by thermal expansion, by whoppingpochard, detailed here: [Extrusion Backers](../../whoppingpochard/extrusion_backers)
+
+If the stock X rails are replaced with a single MGN12 rail ([MGN12 Mod](../../arkeet/mgn12)), that leaves two free MGN9 rails which can be used as backers for the Y extrusions.  They do not fit stock as the spacing on top of the extrusion is smaller than on the bottom.  This permits their installation without the need to cut them down.
+
+Includes new Front Idler Uppers, new belt clips and a taller XY Cable Bridge. 
+
+![Idler](IMAGES/Front_Idler_MGN9_Backer.JPG)
+
+![Rails_Installed](IMAGES/Rails_installed.JPG)
+
+![Installed](IMAGES/Rail_with_idler.jpg)
diff --git a/printer_mods/bythorsthunder/MGN9_Backers/STL_Files/[a]_left_upper_belt_clip_MGN9_backer.stl b/printer_mods/bythorsthunder/MGN9_Backers/STL_Files/[a]_left_upper_belt_clip_MGN9_backer.stl
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diff --git a/printer_mods/bythorsthunder/MGN9_Backers/STL_Files/[a]_right_upper_belt_clip_MGN9_backer.stl b/printer_mods/bythorsthunder/MGN9_Backers/STL_Files/[a]_right_upper_belt_clip_MGN9_backer.stl
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diff --git a/printer_mods/bythorsthunder/MGN9_Backers/STL_Files/[a]_xy_chain_bridge_modified.stl b/printer_mods/bythorsthunder/MGN9_Backers/STL_Files/[a]_xy_chain_bridge_modified.stl
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diff --git a/printer_mods/bythorsthunder/MGN9_Backers/STL_Files/left_idler_upper_MGN9_backer.stl b/printer_mods/bythorsthunder/MGN9_Backers/STL_Files/left_idler_upper_MGN9_backer.stl
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diff --git a/printer_mods/bythorsthunder/MGN9_Backers/STL_Files/right_idler_upper_MGN9_backer.stl b/printer_mods/bythorsthunder/MGN9_Backers/STL_Files/right_idler_upper_MGN9_backer.stl
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