Question 1

Are these 0.4mm?

Accepted Answer

I assume you're wanting to know the width of line it can create. -- It Depends on how you use it and on what material...  
The BIC "marker" simply states "ultra fine point". 
            (It is not a ball point.) (The small tip does a good job of resisting deforming/squishing with normal pressure)
I measured the diameter of the "wick" at the tip of pen at ~0.85mm, but that then rounds off at the end where it would touch a surface. 
A drawn line width would depend on the material: plastic, paper (lots of types of paper), etc... (how much ink is absorbed or deposited and how fast.)
I took a "post-it note" paper and drew some "test" lines:   [(using a metal ruler, with the ruler edge itself not touching the paper(thin cork spacer underneath the ruler)]
   -A "slow" drawn line lets more ink get absorbed into the paper, and the line is thicker and darker: (~0.5mm)  line. 
   - A very "fast" drawn line (the thinnest/lightest I could make it, and still have it all appear the same consistency)- I measured with digital caliper at ~0.35mm thickness. 
   - If I let the tip rest a moment on the paper at either the start or end of a line, then it will of course leave a larger "dot" at that point, due to more ink soaking into the paper. I didn't test it on other substances.
I measured by shining a bright light from underneath through the paper (to make the line easy to see with no shadows), and measured the line thickness best as I could with digital caliper on top of paper. 
note: The pen doesn't have a longer straight metal guide for the tip "wick" to feed through. (gotta be a technical term for that, but wick will suffice)

If it needs to follow a thin template slot, the plastic guide just above the tip holding the wick, I measured at ~1.2mm thick, and it's ~1.6mm long including to the end of the tip itself. 
(so a template would need a slot >1.2mm wide, and less than ~1.6mm thick for the pen tip to reach the surface.) 
  -- but most of that type of drawing is now done with computer/drafting etc. programs, so no finesse required in this respect. 
 ++ Hope that helps.

Question 2

can you write on a canvas print with this?

Accepted Answer

Although I've never written specifically on a canvas print, I don't doubt that it would write well.  My disappointment with this pen was that it was marked "fine point" and I expect that to be a pretty fine line.  However, my "fine points" are well into the "medium" group as far as I'm concerned.  So, it depends on what width of line you're looking for, but don't expect the "Fine" to be anything but "fine."  They would show up conspicuously on a canvas print in my opinion.

Question 3

Will these work on Rite in the Rain paper?'

Accepted Answer

I don't know what Rite in the Rain Paper is, but it will not smear if that helps.

Question 4

Can they be used for fabrics?

Accepted Answer

This is what I found out:
Tips. When using permanent marker on fabric, opt for a 100% natural fiber fabric, such as cotton or linen. Natural fibers absorb the ink better than synthetic fibers, such as polyester.  Also, in addition to permanent markers, fabric markers are a good choice because they're designed to hold up to many washings.

ASIN	B0000AQOCK
Additional Features	Non Toxic
Age Range Description	Adult
Best Sellers Rank	#2,328 in Office Products ( See Top 100 in Office Products ) #50 in Permanent Markers & Marker Pens
Body Shape	Cylindrical
Brand	BIC
Brand Name	BIC
Color	Ultra Fine Tip Black Ink Markers
Customer Reviews	4.7 out of 5 stars 1,491 Reviews
Grip Type	Contoured
Hand Orientation	Ambidextrous
Included Components	12 black permanent markers
Ink Base	Oil
Ink Color	Black
Is Waterproof	true
Item Dimensions	1.44 x 5.5 x 2.75 inches
Item Dimensions D x W x H	2.8"D x 5.5"W x 1.6"H
Item Weight	0.21 Pounds
Line Size	0.3mm
Manufacturer	BIC Corporation
Manufacturer Part Number	GPMU11-BLK
Marker Type	Permanent Marker
Material Type	Rubber
Model Number	GPMU11-BLACK
Number of Items	1
Number of Pieces	12
Pattern	Solid
Point Type	Fine
Recommended Uses For Product	Glass,Plastic
Style	Ultra Fine Point
Surface Recommendation	Metal
Target Audience	Adult
Theme	Artistic Creation
UPC	070330319318
Unit Count	12.0 Count
Warranty Description	100%
Water Resistance Level	Water Resistant
Writing Instrument Form	Marker Pen
Writing Technique	Fine tip

Intensity Black Permanent Markers, Ultra Fine Point, 12-Count Pack of Black Markers With Non-Slip Grip for Comfort and Control

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