This is the first time I’ve ever heard of this pencil. Apparently it has a digital clock? Tip looks to have a siding sleeve. I don’t know what lead diameter it could use, perhaps 0.5mm.
Here’s a current listing.
Below is a picture from Google of the Windom in its case.
I don’t think that’s an actual Pentel piece.
Bat signal for @nimrodd or @knocktype11
Looks like a Cross pen to me. The clip really screams Cross.
The more I look at this the less I think it is a Cross pencil and the more I think it is not a Pentel pencil either. Maybe an early to mid 80’s trash pencil.
Stop looking at it so much. 
The design looks to be a body knock pencil from Kokuyo’s later Mistral line. This design was also licensed to rOtring in the late 90s-early 2000s. Addition of a digital clock seems to be targeted at students taking their university entrance exams. Seriously doubt it’s a Pentel.
Photo 7 on the listing has paperwork, and nowhere on there do I see Pentel (ぺんてる).
has anyone found how to install batteries (for that matter, what size battery) and set the clock on the Windom? Maybe there is a PEN with similar clock that has instructions?
I just found an auction that definitively marks this as a Pentel.
This is a set of the Burgundy Windom Pencil and Pentel set. If you check out image 4, you will see the pen marked as Pentel.
Maybe the instruction sheet will reveal more
I got my Windoms in today and found hoy to change the battery. Pull the pieces apart (don’t unscrew). Then up by the clock you will see a spring holding the battery/batteries in.
I have not pulled the battery yet, but it appears to be an SR4W.
The pen is model number BWD1.
Can you please post a picture when you have time?
Here is the set I just purchased.
For the pen, it doesn’t unscrew, so just pull the back off to get to the battery compartment. The ink is replaced from the tip.
On both the pencil and the pen, the front (clip side) says “Windom”.
On the back of the pencil, it has 0.5 (in Pentel font) over Japan.
On the back of the pen, it says “Pentel BWD1” over Japan.
I replaced the batteries on both of these, but they did not come back on. Both batteries that were in there had minor corrosion on the negative terminal. I tried cleaning them with a little bit of baking soda and water, but I may need to make a better paste and put in there for a bit.
Thanks Jimmy @nimrodd
I’ve got my battery ordered!
What does the inside of the silver piece look like? On mine it has a white plastic part at the bottom that has the cone shape which helps knock the pencil when bent. Here is a video looking down into mine. I have tried using a small hook to catch the area under the threads but it’s not budging
Screw the grip back on, then just pull it apart.
After the silver part is pulled out, the hook is to pull out the spring holding the battery in.
Well I’ll be dammed, I just wasn’t pulling hard enough - thanks -
Lots going on today but later tonight or tomorrow I’ll try to get the battery replaced
I guess you pulled hard enough?
