diff --git a/Marlin/Marlin.h b/Marlin/Marlin.h
index 524a0cac7..3cbf06541 100644
--- a/Marlin/Marlin.h
+++ b/Marlin/Marlin.h
@@ -386,16 +386,6 @@ void report_current_position();
   void set_z_fade_height(const float zfh, const bool do_report=true);
 #endif
 
-#if ENABLED(X_DUAL_ENDSTOPS)
-  extern float x_endstop_adj;
-#endif
-#if ENABLED(Y_DUAL_ENDSTOPS)
-  extern float y_endstop_adj;
-#endif
-#if ENABLED(Z_DUAL_ENDSTOPS)
-  extern float z_endstop_adj;
-#endif
-
 #if HAS_BED_PROBE
   extern float zprobe_zoffset;
   bool set_probe_deployed(const bool deploy);
diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index 5913c8f2e..56a5be713 100644
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -205,7 +205,7 @@
  * M603 - Configure filament change: "M603 T<tool> U<unload_length> L<load_length>". (Requires ADVANCED_PAUSE_FEATURE)
  * M605 - Set Dual X-Carriage movement mode: "M605 S<mode> [X<x_offset>] [R<temp_offset>]". (Requires DUAL_X_CARRIAGE)
  * M665 - Set delta configurations: "M665 L<diagonal rod> R<delta radius> S<segments/s> A<rod A trim mm> B<rod B trim mm> C<rod C trim mm> I<tower A trim angle> J<tower B trim angle> K<tower C trim angle>" (Requires DELTA)
- * M666 - Set/get offsets for delta (Requires DELTA) or dual endstops (Requires [XYZ]_DUAL_ENDSTOPS).
+ * M666 - Set/get endstop offsets for delta (Requires DELTA) or dual endstops (Requires [XYZ]_DUAL_ENDSTOPS).
  * M701 - Load filament (requires FILAMENT_LOAD_UNLOAD_GCODES)
  * M702 - Unload filament (requires FILAMENT_LOAD_UNLOAD_GCODES)
  * M851 - Set Z probe's Z offset in current units. (Negative = below the nozzle.)
@@ -565,16 +565,6 @@ uint8_t target_extruder;
   #define ADJUST_DELTA(V) NOOP
 #endif
 
-#if ENABLED(X_DUAL_ENDSTOPS)
-  float x_endstop_adj;                // Initialized by settings.load()
-#endif
-#if ENABLED(Y_DUAL_ENDSTOPS)
-  float y_endstop_adj;                // Initialized by settings.load()
-#endif
-#if ENABLED(Z_DUAL_ENDSTOPS)
-  float z_endstop_adj;                // Initialized by settings.load()
-#endif
-
 // Extruder offsets
 #if HOTENDS > 1
   float hotend_offset[XYZ][HOTENDS];  // Initialized by settings.load()
@@ -3030,8 +3020,8 @@ static void homeaxis(const AxisEnum axis) {
     const bool pos_dir = axis_home_dir > 0;
     #if ENABLED(X_DUAL_ENDSTOPS)
       if (axis == X_AXIS) {
-        const bool lock_x1 = pos_dir ? (x_endstop_adj > 0) : (x_endstop_adj < 0);
-        const float adj = FABS(x_endstop_adj);
+        const bool lock_x1 = pos_dir ? (endstops.x_endstop_adj > 0) : (endstops.x_endstop_adj < 0);
+        const float adj = FABS(endstops.x_endstop_adj);
         if (lock_x1) stepper.set_x_lock(true); else stepper.set_x2_lock(true);
         do_homing_move(axis, pos_dir ? -adj : adj);
         if (lock_x1) stepper.set_x_lock(false); else stepper.set_x2_lock(false);
@@ -3040,8 +3030,8 @@ static void homeaxis(const AxisEnum axis) {
     #endif
     #if ENABLED(Y_DUAL_ENDSTOPS)
       if (axis == Y_AXIS) {
-        const bool lock_y1 = pos_dir ? (y_endstop_adj > 0) : (y_endstop_adj < 0);
-        const float adj = FABS(y_endstop_adj);
+        const bool lock_y1 = pos_dir ? (endstops.y_endstop_adj > 0) : (endstops.y_endstop_adj < 0);
+        const float adj = FABS(endstops.y_endstop_adj);
         if (lock_y1) stepper.set_y_lock(true); else stepper.set_y2_lock(true);
         do_homing_move(axis, pos_dir ? -adj : adj);
         if (lock_y1) stepper.set_y_lock(false); else stepper.set_y2_lock(false);
@@ -3050,8 +3040,8 @@ static void homeaxis(const AxisEnum axis) {
     #endif
     #if ENABLED(Z_DUAL_ENDSTOPS)
       if (axis == Z_AXIS) {
-        const bool lock_z1 = pos_dir ? (z_endstop_adj > 0) : (z_endstop_adj < 0);
-        const float adj = FABS(z_endstop_adj);
+        const bool lock_z1 = pos_dir ? (endstops.z_endstop_adj > 0) : (endstops.z_endstop_adj < 0);
+        const float adj = FABS(endstops.z_endstop_adj);
         if (lock_z1) stepper.set_z_lock(true); else stepper.set_z2_lock(true);
         do_homing_move(axis, pos_dir ? -adj : adj);
         if (lock_z1) stepper.set_z_lock(false); else stepper.set_z2_lock(false);
@@ -9021,26 +9011,45 @@ inline void gcode_M205() {
 #elif ENABLED(X_DUAL_ENDSTOPS) || ENABLED(Y_DUAL_ENDSTOPS) || ENABLED(Z_DUAL_ENDSTOPS)
 
   /**
-   * M666: For Z Dual Endstop setup, set z axis offset to the z2 axis.
+   * M666: Set Dual Endstops offsets for X, Y, and/or Z.
+   *       With no parameters report current offsets.
    */
   inline void gcode_M666() {
-    SERIAL_ECHOPGM("Dual Endstop Adjustment (mm): ");
+    bool report = true;
     #if ENABLED(X_DUAL_ENDSTOPS)
-      if (parser.seen('X')) x_endstop_adj = parser.value_linear_units();
-      SERIAL_ECHOPAIR(" X", x_endstop_adj);
+      if (parser.seenval('X')) {
+        endstops.x_endstop_adj = parser.value_linear_units();
+        report = false;
+      }
     #endif
     #if ENABLED(Y_DUAL_ENDSTOPS)
-      if (parser.seen('Y')) y_endstop_adj = parser.value_linear_units();
-      SERIAL_ECHOPAIR(" Y", y_endstop_adj);
+      if (parser.seenval('Y')) {
+        endstops.y_endstop_adj = parser.value_linear_units();
+        report = false;
+      }
     #endif
     #if ENABLED(Z_DUAL_ENDSTOPS)
-      if (parser.seen('Z')) z_endstop_adj = parser.value_linear_units();
-      SERIAL_ECHOPAIR(" Z", z_endstop_adj);
+      if (parser.seenval('Z')) {
+        endstops.z_endstop_adj = parser.value_linear_units();
+        report = false;
+      }
     #endif
-    SERIAL_EOL();
+    if (report) {
+      SERIAL_ECHOPGM("Dual Endstop Adjustment (mm): ");
+      #if ENABLED(X_DUAL_ENDSTOPS)
+        SERIAL_ECHOPAIR(" X", endstops.x_endstop_adj);
+      #endif
+      #if ENABLED(Y_DUAL_ENDSTOPS)
+        SERIAL_ECHOPAIR(" Y", endstops.y_endstop_adj);
+      #endif
+      #if ENABLED(Z_DUAL_ENDSTOPS)
+        SERIAL_ECHOPAIR(" Z", endstops.z_endstop_adj);
+      #endif
+      SERIAL_EOL();
+    }
   }
 
-#endif // !DELTA && Z_DUAL_ENDSTOPS
+#endif // X_DUAL_ENDSTOPS || Y_DUAL_ENDSTOPS || Z_DUAL_ENDSTOPS
 
 #if ENABLED(FWRETRACT)
 
diff --git a/Marlin/configuration_store.cpp b/Marlin/configuration_store.cpp
index fbde923ea..1d78a6a74 100644
--- a/Marlin/configuration_store.cpp
+++ b/Marlin/configuration_store.cpp
@@ -546,19 +546,19 @@ void MarlinSettings::postprocess() {
       // Write dual endstops in X, Y, Z order. Unused = 0.0
       dummy = 0.0f;
       #if ENABLED(X_DUAL_ENDSTOPS)
-        EEPROM_WRITE(x_endstop_adj);             // 1 float
+        EEPROM_WRITE(endstops.x_endstop_adj);   // 1 float
       #else
         EEPROM_WRITE(dummy);
       #endif
 
       #if ENABLED(Y_DUAL_ENDSTOPS)
-        EEPROM_WRITE(y_endstop_adj);             // 1 float
+        EEPROM_WRITE(endstops.y_endstop_adj);   // 1 float
       #else
         EEPROM_WRITE(dummy);
       #endif
 
       #if ENABLED(Z_DUAL_ENDSTOPS)
-        EEPROM_WRITE(z_endstop_adj);             // 1 float
+        EEPROM_WRITE(endstops.z_endstop_adj);   // 1 float
       #else
         EEPROM_WRITE(dummy);
       #endif
@@ -1070,17 +1070,17 @@ void MarlinSettings::postprocess() {
         _FIELD_TEST(x_endstop_adj);
 
         #if ENABLED(X_DUAL_ENDSTOPS)
-          EEPROM_READ(x_endstop_adj);             // 1 float
+          EEPROM_READ(endstops.x_endstop_adj);  // 1 float
         #else
           EEPROM_READ(dummy);
         #endif
         #if ENABLED(Y_DUAL_ENDSTOPS)
-          EEPROM_READ(y_endstop_adj);             // 1 float
+          EEPROM_READ(endstops.y_endstop_adj);  // 1 float
         #else
           EEPROM_READ(dummy);
         #endif
         #if ENABLED(Z_DUAL_ENDSTOPS)
-          EEPROM_READ(z_endstop_adj);             // 1 float
+          EEPROM_READ(endstops.z_endstop_adj); // 1 float
         #else
           EEPROM_READ(dummy);
         #endif
@@ -1638,7 +1638,7 @@ void MarlinSettings::reset() {
   #elif ENABLED(X_DUAL_ENDSTOPS) || ENABLED(Y_DUAL_ENDSTOPS) || ENABLED(Z_DUAL_ENDSTOPS)
 
     #if ENABLED(X_DUAL_ENDSTOPS)
-      x_endstop_adj = (
+      endstops.x_endstop_adj = (
         #ifdef X_DUAL_ENDSTOPS_ADJUSTMENT
           X_DUAL_ENDSTOPS_ADJUSTMENT
         #else
@@ -1647,7 +1647,7 @@ void MarlinSettings::reset() {
       );
     #endif
     #if ENABLED(Y_DUAL_ENDSTOPS)
-      y_endstop_adj = (
+      endstops.y_endstop_adj = (
         #ifdef Y_DUAL_ENDSTOPS_ADJUSTMENT
           Y_DUAL_ENDSTOPS_ADJUSTMENT
         #else
@@ -1656,7 +1656,7 @@ void MarlinSettings::reset() {
       );
     #endif
     #if ENABLED(Z_DUAL_ENDSTOPS)
-      z_endstop_adj = (
+      endstops.z_endstop_adj = (
         #ifdef Z_DUAL_ENDSTOPS_ADJUSTMENT
           Z_DUAL_ENDSTOPS_ADJUSTMENT
         #else
@@ -2140,13 +2140,13 @@ void MarlinSettings::reset() {
       CONFIG_ECHO_START;
       SERIAL_ECHOPGM("  M666");
       #if ENABLED(X_DUAL_ENDSTOPS)
-        SERIAL_ECHOPAIR(" X", LINEAR_UNIT(x_endstop_adj));
+        SERIAL_ECHOPAIR(" X", LINEAR_UNIT(endstops.x_endstop_adj));
       #endif
       #if ENABLED(Y_DUAL_ENDSTOPS)
-        SERIAL_ECHOPAIR(" Y", LINEAR_UNIT(y_endstop_adj));
+        SERIAL_ECHOPAIR(" Y", LINEAR_UNIT(endstops.y_endstop_adj));
       #endif
       #if ENABLED(Z_DUAL_ENDSTOPS)
-        SERIAL_ECHOPAIR(" Z", LINEAR_UNIT(z_endstop_adj));
+        SERIAL_ECHOPAIR(" Z", LINEAR_UNIT(endstops.z_endstop_adj));
       #endif
       SERIAL_EOL();
     #endif // DELTA
diff --git a/Marlin/endstops.cpp b/Marlin/endstops.cpp
index 6dc0b9c9f..a7edfa4b9 100644
--- a/Marlin/endstops.cpp
+++ b/Marlin/endstops.cpp
@@ -41,18 +41,24 @@ Endstops endstops;
 bool Endstops::enabled, Endstops::enabled_globally; // Initialized by settings.load()
 volatile char Endstops::endstop_hit_bits; // use X_MIN, Y_MIN, Z_MIN and Z_MIN_PROBE as BIT value
 
-#if ENABLED(X_DUAL_ENDSTOPS) || ENABLED(Y_DUAL_ENDSTOPS) || ENABLED(Z_DUAL_ENDSTOPS)
-  uint16_t
-#else
-  byte
-#endif
-    Endstops::current_endstop_bits = 0,
-    Endstops::old_endstop_bits = 0;
+Endstops::esbits_t Endstops::current_endstop_bits = 0,
+                   Endstops::old_endstop_bits = 0;
 
 #if HAS_BED_PROBE
   volatile bool Endstops::z_probe_enabled = false;
 #endif
 
+// Initialized by settings.load()
+#if ENABLED(X_DUAL_ENDSTOPS)
+  float Endstops::x_endstop_adj;
+#endif
+#if ENABLED(Y_DUAL_ENDSTOPS)
+  float Endstops::y_endstop_adj;
+#endif
+#if ENABLED(Z_DUAL_ENDSTOPS)
+  float Endstops::z_endstop_adj;
+#endif
+
 /**
  * Class and Instance Methods
  */
@@ -269,7 +275,7 @@ void Endstops::M119() {
 
 #if ENABLED(X_DUAL_ENDSTOPS)
   void Endstops::test_dual_x_endstops(const EndstopEnum es1, const EndstopEnum es2) {
-    byte x_test = TEST_ENDSTOP(es1) | (TEST_ENDSTOP(es2) << 1); // bit 0 for X, bit 1 for X2
+    const byte x_test = TEST_ENDSTOP(es1) | (TEST_ENDSTOP(es2) << 1); // bit 0 for X, bit 1 for X2
     if (x_test && stepper.current_block->steps[X_AXIS] > 0) {
       SBI(endstop_hit_bits, X_MIN);
       if (!stepper.performing_homing || (x_test == 0x3))  //if not performing home or if both endstops were trigged during homing...
@@ -279,7 +285,7 @@ void Endstops::M119() {
 #endif
 #if ENABLED(Y_DUAL_ENDSTOPS)
   void Endstops::test_dual_y_endstops(const EndstopEnum es1, const EndstopEnum es2) {
-    byte y_test = TEST_ENDSTOP(es1) | (TEST_ENDSTOP(es2) << 1); // bit 0 for Y, bit 1 for Y2
+    const byte y_test = TEST_ENDSTOP(es1) | (TEST_ENDSTOP(es2) << 1); // bit 0 for Y, bit 1 for Y2
     if (y_test && stepper.current_block->steps[Y_AXIS] > 0) {
       SBI(endstop_hit_bits, Y_MIN);
       if (!stepper.performing_homing || (y_test == 0x3))  //if not performing home or if both endstops were trigged during homing...
@@ -289,7 +295,7 @@ void Endstops::M119() {
 #endif
 #if ENABLED(Z_DUAL_ENDSTOPS)
   void Endstops::test_dual_z_endstops(const EndstopEnum es1, const EndstopEnum es2) {
-    byte z_test = TEST_ENDSTOP(es1) | (TEST_ENDSTOP(es2) << 1); // bit 0 for Z, bit 1 for Z2
+    const byte z_test = TEST_ENDSTOP(es1) | (TEST_ENDSTOP(es2) << 1); // bit 0 for Z, bit 1 for Z2
     if (z_test && stepper.current_block->steps[Z_AXIS] > 0) {
       SBI(endstop_hit_bits, Z_MIN);
       if (!stepper.performing_homing || (z_test == 0x3))  //if not performing home or if both endstops were trigged during homing...
diff --git a/Marlin/endstops.h b/Marlin/endstops.h
index e60132d6e..96cb3d089 100644
--- a/Marlin/endstops.h
+++ b/Marlin/endstops.h
@@ -21,11 +21,11 @@
  */
 
 /**
- *  endstops.h - manages endstops
+ * endstops.h - manages endstops
  */
 
-#ifndef ENDSTOPS_H
-#define ENDSTOPS_H
+#ifndef __ENDSTOPS_H__
+#define __ENDSTOPS_H__
 
 #include "enum.h"
 #include "MarlinConfig.h"
@@ -38,11 +38,21 @@ class Endstops {
     static volatile char endstop_hit_bits; // use X_MIN, Y_MIN, Z_MIN and Z_MIN_PROBE as BIT value
 
     #if ENABLED(X_DUAL_ENDSTOPS) || ENABLED(Y_DUAL_ENDSTOPS) || ENABLED(Z_DUAL_ENDSTOPS)
-      static uint16_t
+      typedef uint16_t esbits_t;
+      #if ENABLED(X_DUAL_ENDSTOPS)
+        static float x_endstop_adj;
+      #endif
+      #if ENABLED(Y_DUAL_ENDSTOPS)
+        static float y_endstop_adj;
+      #endif
+      #if ENABLED(Z_DUAL_ENDSTOPS)
+        static float z_endstop_adj;
+      #endif
     #else
-      static byte
+      typedef byte esbits_t;
     #endif
-        current_endstop_bits, old_endstop_bits;
+
+    static esbits_t current_endstop_bits, old_endstop_bits;
 
     Endstops() {
       enable_globally(
@@ -57,7 +67,7 @@ class Endstops {
     /**
      * Initialize the endstop pins
      */
-    void init();
+    static void init();
 
     /**
      * Update the endstops bits from the pins
@@ -113,5 +123,4 @@ extern Endstops endstops;
   #define ENDSTOPS_ENABLED  endstops.enabled
 #endif
 
-
-#endif // ENDSTOPS_H
+#endif // __ENDSTOPS_H__