Dear Gus,
So long as you experience "no change" in the feel of your hands on the grip during the stroke, you're probably fine. The purpose of the flat-top grip form is for golfers who want an extra way to secure the hands to the handle, as the thumb is key to most human grip patterns (you know, the "opposable thumbs" that make humans better than chimps, and all that).
Historically, "flat top" golf grips date from at least 1928. This
1928 William Harness Patent has a flat-top grip for both a putter and a driver.
The idea is to press the puffy flesh of the thumb tip onto the flat surface, as the handle is supposed to be glued onto the shaft so that the flat part is oriented square to the aim of the putter head. (You better check this, as I find lots of off-the-shelf putters don't quite have square handles.) Then, if the putter head opens or closes during the stroke in relation to the stroke path, the golfer will "feel" a differential pressure on one side or the other of the thumb tip's contact area with the surface, and this difference alerts the golfer to a need to do something to resquare the putter head coming into and thru impact. (One way to make a cut stroke is for the putter head to flare open going back and then the golfer just keeps the face open coming thru, but on a slightly out-to-in path thru impact.)
Another use of the flat surface is for golfers wanting a straight-back, straight-thru stroke path -- keeping the putter head square to the line and also square to the path -- whether the stroke motion is a vertical plane or a tilted plane parallel to the line of the putt. In this case, the golfer pays attention to the feel of the handle surface in space to "keep it" parallel to the line of the putt and the parallel plane of motion of the stroke. This is the same feeling you would have if you held a business card in between your thumbs and the middle knuckle of your index fingers, aligning the top edge of the card with the aim of the putter, and then moving the hands back and thru so that the top edge of the card stayed parallel to the line of the putt the whole time.
And a third use of the thumbs on the putter handle is to "firm up" the shape of the hand, to make the hand and wrist less active during the stroke. George Low in the 1960s-1980s taught that he would "dig" his thumb nails into the handle. This is certainly partly in order to keep the putter head from opening or closing out of the stroke path, but it is also more than that. To "dig" the thumb nail requires exerting opposing pressure back against the thumb by the fingers on the underside of the handle, to squeeze the handle in between the parts of the hand. The muscle tension in the hand that accomplishes this squeezing also serves to "firm up" the connection between the hand and the forearm thru the tendons and muscle connections in the forearm that operate the hand. The effect is to "firm up" the shape of the hand and the wrist, making it less likely that there will be independent motions of the hands and wrists during the stroke that are not coordinated with the stroke motion of the shoulders, or the "triangle" as a whole unit. In this same vein, some teachers advise a little tightening of the last three fingers of each hand, matching a thumb-side pressure with a pinky-side pressure to even out the grip pressure throughout the whole hand, making the hands more of a solid, unchanging unit.
A fourth function of the flat-top surface is to assist the golfer in a certain impact dynamic. In 1941 golfing great Al Espinoza created the "pistol grip" for putters:
The claimed benefit was to restrict the tendency to push the ball instead of striking it during the stroke. To me, this means the grip form works to make the actual impact dynamics more of a square impact -- one in which the putter face remains square while the putter face and ball are still in contact -- as opposed to a dynamic in which the putter face is "arcing" thru impact and changing direction while the putter face and ball are still in contact. It would appear that you have taught yourself this square "strike" dynamics (Espinoza's term, not mine), so it is not your problem. Strictly speaking, the "pistol" grip refers to the contouring of the underside of the grip, but typically pistol grips also feature a flat top.
A fifth function is using the flat surface to help align both thumbs straight down the handle and shaft, as in this picture / drwaing:
You can see that both thumb lines are the same, or at least parallel to each other, and that both lines match the line of the shaft. This accompanies pressing the thumb pad flat to the surface, as the tumb pad is an oval with the long-axis the same as the line of the thumb heel of thumb to tip of thumb. This creates angles between the lines of the thumbs and the forearms (see above). The maintaining of these angles thru the stroke suppresses wristiness. This has the same effect as the drill of wedging a golf ball between the handle and the lead forearm, keeping the ball securely in place throughout the stroke.
Recently, grips have been made in a fashion allowing both thumbs to rest on the handle side-by-side by making the top surface of the grip wider. This is the case with the
Pure Pendulum putters and the Two Thumbs grip (pictured here):
This style dates from at least 1977 -- see
Jack Key's 1977 patent.
In the case of standard or conventional grips,
Golf Pride offers eight putter grips, all with a "flat front";
Winn Grips offers seven grips all with a flat top and also offers a flat-top belly putter grip;
Lamkin Grips offers ten styles, nine of which have flat tops, and one has a round profile with a pistol-grip underside; and
Tacki-Mac Grips offers ten styles, all with flat tops in varying degrees.
There are different degrees of sharpness in defining the edges of these "flat tops", with some style grips having very sharply defined edges. Sharp left and right edges to the flat top can be used sort of like the rudder on a sail boat -- if you tend to let the putter face flare open going back, placing the left thumb tip onto the left edge with a little extra pressure is a way to prevent or retard this opening, and for this a sharper edge helps the "feel" control. Similarly, if you tend to pull your putts, closing the face too much thru impact, then placing the right thumb on the right edge with a little extra pressure can help prevent this as well.
Of course, none of this hands stuff will prevent a pull or a push or a cut stroke, as all of these can occur regardless of keeping the putter head square to the stroke path. There is still the problem of getting the stroke path to go as and where you want it. This means that you can certainly make an effective stroke without a flat-top handle, as you well know. It's just a case of grip companies trying to be "helpful". In this case, the flat-top handle is generally helpful without being strictly necessary.
Cheers!
Geoff Mangum
Putting Coach and Theorist
PuttingZone
http://puttingzone.com
Golf's most advanced putting instruction -- you're either in the PuttingZone, or not.
