Index: trunk/pcblib/parametric/screw
===================================================================
--- trunk/pcblib/parametric/screw	(revision 894)
+++ trunk/pcblib/parametric/screw	(revision 895)
@@ -7,10 +7,11 @@
 #@@desc Generate a "single pin" screw with optional head shapes
 #@@params hole,head,shape,ring
 
-#@@param:hole hole diameter
+#@@param:hole hole diameter or name of a standard screw (e.g. M3)
 #@@dim:hole
 
-#@@param:head head outmost diameter
+
+#@@param:head head outmost diameter (or optional head name for a standard screw: pan, button, cheese, flat-washer, internal-lock-washer)
 #@@dim:head
 
 #@@param:ring copper ring outer diameter
Index: trunk/pcblib/parametric/screw.awk
===================================================================
--- trunk/pcblib/parametric/screw.awk	(revision 894)
+++ trunk/pcblib/parametric/screw.awk	(revision 895)
@@ -41,15 +41,55 @@
 	}
 }
 
+function round_up(num, to)
+{
+	if ((num/to) == int(num/to))
+		return num
+	return int(num/to+1)*to
+}
+
 BEGIN {
 	set_arg(P, "?shape", "circle")
-	proc_args(P, "hole,head,shape,ring", "hole,head")
+	proc_args(P, "hole,head,shape,ring", "hole")
 
 	element_begin("", "S1", "screw:" P["hole"] "," P["head"]"," P["shape"]    ,0,0, 0, mil(-100))
 
-	hole = parse_dim(P["hole"])
-	head = parse_dim(P["head"])
+	if (P["hole"] ~ "^M") {
+		hole = P["hole"]
+		sub("^M", "", hole)
+		h = parse_dim(int(hole) "mm")
+		if ((hole ~ "tight") || (hole ~ "close.fit"))
+			hole = h * 1.05
+		else
+			hole = h * 1.1
+		hd = parse_dim(P["head"])
+		if (hd == 0) {
+			hd = P["head"]
+			if (hd == "button")
+				head = 1.9*h 
+			else if (hd == "button")
+				head = 1.9*h 
+			else if (hd == "cheese")
+				head = round_up(1.7*h, mm(0.5))
+			else if (hd ~ "flat.washer")
+				head = round_up(2.1*h, mm(1))
+			else if ((hd == "") || (hd == "pan") || (hd ~ "int.*.lock.washer"))
+				head = 2*h
+			else
+				error("Unknown standard head: " hd)
+		}
+		else
+			head = hd
+		print hole, head > "/dev/stderr"
+	}
+	else {
+		hole = parse_dim(P["hole"])
+		head = parse_dim(P["head"])
+	}
 
+	if (head == "")
+		error("need a standard screw name, e.g. M3, or a head diameter")
+
 	if (head < hole)
 		error("head diameter must be larger than hole diameter")