diff --git a/readme.md b/readme.md
index 0ba4822..3ba9b6f 100644
--- a/readme.md
+++ b/readme.md
@@ -3019,7 +3019,7 @@ Potentiometers and rotary encoders
 | `pot_spigot_x(type)` | Spigot offset from the shaft centre |
 | `pot_thread_d(type)` | Nomininal thread diameter |
 | `pot_thread_h(type)` | Height of threaded part |
-| `pot_thread_p(type)` | Thread pritch |
+| `pot_thread_p(type)` | Thread pitch |
 | `pot_wafer(type)` | Width, diameter and thickness of the track wafer plus true if curved |
 | `pot_washer(type)` | Outside diameter and thickness of the washer |
 
@@ -3512,7 +3512,7 @@ For an explanation of `screw_polysink()` see <https://hydraraptor.blogspot.com/2
 | `screw_radius(type)` | Nominal radius |
 | `screw_socket_af(type)` | Socket across flats |
 | `screw_socket_depth(type)` | Socket or slot depth |
-| `screw_thread_diameter(type)` | Thread diameter, if different from nominal diamter |
+| `screw_thread_diameter(type)` | Thread diameter, if different from nominal diameter |
 | `screw_washer(type)` | Default washer |
 
 ### Functions
diff --git a/tests/png/fan_guard.png b/tests/png/fan_guard.png
index 138d096..4745f36 100644
Binary files a/tests/png/fan_guard.png and b/tests/png/fan_guard.png differ
diff --git a/tests/png/green_terminals.png b/tests/png/green_terminals.png
index ebae486..9ce55a3 100644
Binary files a/tests/png/green_terminals.png and b/tests/png/green_terminals.png differ
diff --git a/vitamins/screw.scad b/vitamins/screw.scad
index badf8e9..3bc1cbe 100644
--- a/vitamins/screw.scad
+++ b/vitamins/screw.scad
@@ -41,7 +41,7 @@ function screw_washer(type)           = type[9];     //! Default washer
 function screw_nut(type)              = type[10];    //! Default nut
 function screw_pilot_hole(type)       = type[11];    //! Pilot hole radius for wood screws, tap radius for machine screws
 function screw_clearance_radius(type) = type[12];    //! Clearance hole radius
-function screw_thread_diameter(type)  = type[13];    //! Thread diameter, if different from nominal diamter
+function screw_thread_diameter(type)  = type[13];    //! Thread diameter, if different from nominal diameter
 function screw_nut_radius(type) = screw_nut(type) ? nut_radius(screw_nut(type)) : 0; //! Radius of matching nut
 function screw_boss_diameter(type) = max(washer_diameter(screw_washer(type)) + 1, 2 * (screw_nut_radius(type) + 3 * extrusion_width)); //! Boss big enough for nut trap and washer
 function screw_head_depth(type, d = 0) =             //! How far a counter sink head will go into a straight hole diameter d