diff --git a/modules/reactor/src/meshgenerators/AssemblyMeshGenerator.C b/modules/reactor/src/meshgenerators/AssemblyMeshGenerator.C
index b1d75d8ff026..dc83b559eb10 100644
--- a/modules/reactor/src/meshgenerators/AssemblyMeshGenerator.C
+++ b/modules/reactor/src/meshgenerators/AssemblyMeshGenerator.C
@@ -612,6 +612,8 @@ AssemblyMeshGenerator::generate()
         elem_block_name += "_" + _background_block_name[z_id];
       else if (!is_background_region && _has_duct_block_names)
         elem_block_name += "_" + _duct_block_names[z_id][peripheral_idx - 1];
+      if (elem->type() == TRI3 || elem->type() == PRISM6)
+        elem_block_name += RGMB::TRI_BLOCK_NAME_SUFFIX;
       updateElementBlockNameId(
           *(*_build_mesh), elem, rgmb_name_id_map, elem_block_name, next_block_id);
     }
diff --git a/modules/reactor/test/tests/meshgenerators/assembly_mesh_generator/assembly_hex_flexible.i b/modules/reactor/test/tests/meshgenerators/assembly_mesh_generator/assembly_hex_flexible.i
new file mode 100644
index 000000000000..beab4c55e499
--- /dev/null
+++ b/modules/reactor/test/tests/meshgenerators/assembly_mesh_generator/assembly_hex_flexible.i
@@ -0,0 +1,88 @@
+[Mesh]
+  [rmp]
+    type = ReactorMeshParams
+    dim = 2
+    geom = "Hex"
+    assembly_pitch = 7.10315
+    flexible_assembly_stitching = true
+    region_id_as_block_name = true
+  []
+
+  [pin1]
+    type = PinMeshGenerator
+    reactor_params = rmp
+    pin_type = 1
+    pitch = 1.42063
+    num_sectors = 2
+    ring_radii = '0.2'
+    duct_halfpitch = '0.68'
+    mesh_intervals = '1 1 1'
+    quad_center_elements = true
+    region_ids='1 2 5'
+  []
+
+  [pin2]
+    type = PinMeshGenerator
+    reactor_params = rmp
+    pin_type = 2
+    pitch = 1.42063
+    num_sectors = 2
+    mesh_intervals = '2'
+    region_ids='3'
+    quad_center_elements = true
+  []
+
+  [amg]
+    type = AssemblyMeshGenerator
+    assembly_type = 1
+    inputs = 'pin1 pin2'
+    pattern = '1 1;
+              1 0 1;
+               1 1'
+    background_intervals = 1
+    background_region_id = '6'
+    duct_halfpitch = '3.5'
+    duct_region_ids = '7'
+    duct_intervals = '1'
+  []
+[]
+
+[Problem]
+  solve = false
+[]
+
+[Executioner]
+  type = Steady
+[]
+
+[Postprocessors]
+  [area_reg1]
+    type = VolumePostprocessor
+    block = "RGMB_ASSEMBLY1_REG1"
+  []
+  [area_reg2]
+    type = VolumePostprocessor
+    block = "RGMB_ASSEMBLY1_REG2"
+  []
+  [area_reg3]
+    type = VolumePostprocessor
+    block = "RGMB_ASSEMBLY1_REG3"
+  []
+  [area_reg5]
+    type = VolumePostprocessor
+    block = "RGMB_ASSEMBLY1_REG5"
+  []
+  [area_reg6]
+    type = VolumePostprocessor
+    block = "RGMB_ASSEMBLY1_REG6"
+  []
+  [area_reg7]
+    type = VolumePostprocessor
+    block = "RGMB_ASSEMBLY1_REG7_TRI"
+  []
+[]
+
+[Outputs]
+  csv = true
+  execute_on = 'FINAL'
+[]
diff --git a/modules/reactor/test/tests/meshgenerators/assembly_mesh_generator/gold/assembly_hex_flexible_out.csv b/modules/reactor/test/tests/meshgenerators/assembly_mesh_generator/gold/assembly_hex_flexible_out.csv
new file mode 100644
index 000000000000..caff02c8d175
--- /dev/null
+++ b/modules/reactor/test/tests/meshgenerators/assembly_mesh_generator/gold/assembly_hex_flexible_out.csv
@@ -0,0 +1,2 @@
+time,area_reg1,area_reg2,area_reg3,area_reg5,area_reg6,area_reg7
+2,0.12566370614359,1.4761368806961,10.486820763413,0.14600287372918,30.200620561455,1.2598417287844
diff --git a/modules/reactor/test/tests/meshgenerators/assembly_mesh_generator/tests b/modules/reactor/test/tests/meshgenerators/assembly_mesh_generator/tests
index 6e7432f3d102..39b3665e9d3d 100755
--- a/modules/reactor/test/tests/meshgenerators/assembly_mesh_generator/tests
+++ b/modules/reactor/test/tests/meshgenerators/assembly_mesh_generator/tests
@@ -65,6 +65,14 @@
     exodiff = 'assembly_ductIDs_in.e'
     recover = false
   []
+  [hex_flexible_stitching]
+    requirement = 'The system shall generate a 2D hexagonal assembly mesh with the outermost duct layer removed and re-meshed with FlexiblePatternGenerator'
+    type = 'CSVDiff'
+    input = 'assembly_hex_flexible.i'
+    csvdiff = 'assembly_hex_flexible_out.csv'
+    recover = false
+    mesh_mode = REPLICATED
+  []
   [hex_metadata_transfer]
     requirement = 'The system shall generate a 2D hexagonal assembly mesh that transfers metadata correctly across RGMB mesh generators'
     type = 'Exodiff'